Edge-on SAR scintillator devices and systems for enhanced SPECT, PET, and Compton gamma cameras

ABSTRACT

The invention provides methods and apparatus for detecting radiation including x-ray, gamma ray, and particle radiation for nuclear medicine, radiographic imaging, material composition analysis, high energy physics, container inspection, mine detection and astronomy. The invention provides detection systems employing one or more detector modules comprising edge-on scintillator detectors with sub-aperture resolution (SAR) capability employed, e.g., in nuclear medicine, such as radiation therapy portal imaging, nuclear remediation, mine detection, container inspection, and high energy physics and astronomy. The invention also provides edge-on imaging probe detectors for use in nuclear medicine, such as radiation therapy portal imaging, or for use in nuclear remediation, mine detection, container inspection, and high energy physics and astronomy.

FIELD OF THE INVENTION

This invention provides novel edge-on sub-aperture resolution (SAR)scintillator detectors, designs and systems for, e.g., enhanced singlephoton emission computed tomography (SPECT) and positron emissiontomography (PET), and Compton gamma cameras employed in nuclearmedicine, such as radiation therapy portal imaging, and for nuclearremediation, mine detection, container inspection, and high energyphysics and astronomy. The invention also provides edge-on imaging probedetectors for use in nuclear medicine, such as radiation therapy portalimaging, or for use in nuclear remediation, mine detection, containerinspection, and high energy physics and astronomy.

BACKGROUND OF THE INVENTION

Two important imaging modalities in nuclear medicine are single photonemission computed tomography (SPECT) and positron emission tomography(PET) in which a fraction of the photons emitted directly or indirectly(through positron annihilation) by a radionuclide distribution within apatient are detected. Typical nuclear medicine studies include but arenot limited to whole body, heart, brain, thyroid, gastro-intestinal, andbreast (scintimammography and positron emission mammography or PEM)imaging.

Image data acquisition in nuclear medicine presents several challengesin addition to constraints imposed by finite acquisition times andpatient exposure restrictions. Most photon energies that are of interestin nuclear medicine are higher than the typical photon energies employedin diagnostic x-ray radiography. In particular, PET involves thedetection of pairs of very high energy photons (511 keV) due toannihilation events.

The direction vectors and energies of non-scattered photons that escapethe body are assumed to be well-defined. Unfortunately, the emission ofphotons from the radionuclide source distribution is non-directional andthe radiation source distribution itself is typically not well-defined.Scattered photons that escape the body may have their energies and/ordirection vectors altered. It is desirable for many applications todiscriminate against scatter radiation reaching the detector based onenergy and/or direction. A Compton-scattered photon suffers an energyloss and change in direction vector whereas a coherent or Rayleighscattered photon only has its direction vector altered. It may bedesirable to only detect radiation with a limited range of directionvectors.

Imaging systems typically offer poor directional discriminationcapability and have finite response times within which to detect events(thereby limiting detection rates). Thus detection systems used innuclear medicine such as gamma (SPECT) cameras (and sometimes PETcameras) employ focused or unfocused collimators, to help define thedirection vectors of detected photons. Compton gamma cameras (based onthe detection of one or more Compton scattered photons) and most PETcameras rely on electronic collimation. (The Compton camera design usesone or more relatively thin, planar semiconductor (often Si or Ge)arrays as Compton scatterers. One implementation uses a scintillatorgamma camera to detect the Compton-scattered photons. Compton gammacameras are still being refined.)

The detection format for conventional SPECT, PET, and Compton gammacameras is “face-on” wherein the radiation entrance surface and readoutsurface are parallel. The majority of clinical SPECT and PET camerasemploy scintillator rather than semiconductor detectors. Althoughsemiconductor detectors may offer superior spatial and energyresolution, scintillators are typically less expensive to grow andprocess, they are highly reliable, they may offer superior stoppingpower, and they may offer faster response times (desirable for PET andtime-of-flight (TOF) PET). Scintillators are employed based onconversion efficiency (that may be energy-dependent ornon-proportional), emission spectrum, decay time and after glow, indexof refraction (IOR), density, material-dependent photon cross sections,the presence of natural or induced radioactivity, and manufacturingcost.

Two common detector geometries used in nuclear medicine imaging are theplanar detector (SPECT and PET) and the ring detector (PET). A basicgamma camera design employs a large, planar array of scintillationcrystals or a single, large, planar scintillation crystal opticallycoupled to an array of photomultiplier tubes (PMTs). A conventionalfocused or unfocused collimator is typically mounted to the face of thegamma camera. This imaging system is then positioned such that theregion of interest containing the source distribution is within thefield of view. It provides a limited degree of spatial resolution andenergy resolution while removing some fraction of scattered radiationthat would otherwise degrade image quality. Unfortunately a substantialfraction of useful unscattered radiation is also attenuated. (Aninfrequently used design replaces the conventional collimator with acoded aperture such as a uniformly redundant array aperture that is alsobased on photon attenuation.) Clinical SPECT systems may use one, two,or three gamma camera detector units.

An alternative (face-on) gamma camera design eliminates the use ofscintillator crystals and PMTs with a planar, modular 2-D CdZnTesemiconductor detector manufactured by butting small, 2-D (pixellated)CdZnTe arrays. Drawbacks to employing 2-D CdZnTe arrays capable of highdetection efficiency include the difficulty of growing thick CdZnTecrystals with acceptable levels of defects and creating low noise, 2-Darray readout structures on CdZnTe crystals.

A limitation of the face-on detection format for SPECT and PET imagingis that properties such as the detection efficiency, spatial resolution,and energy resolution exhibit a noticeable energy dependence. Basicedge-on semiconductor and scintillator detector array designs are beingused as alternatives to face-on detectors for x-ray and gamma rayradiography (digital mammography and high energy industrial imaging) andgamma ray imaging in nuclear medicine (PET). Basic edge-on arraydetector designs are suitable for SPECT and Compton scatter imaging aswell as PET imaging.

Cost-effective implementations of edge-on detector modules are neededfor clinical nuclear medicine imaging systems. Factors to considerinclude the material properties and costs, the active detector area andvolume, the desired spatial, energy, and temporal resolution, and thereadout requirements. Consider an edge-on detector module comprised ofone or more basic edge-on semiconductor or scintillator planar detectors(for example, a linear array of scintillator rods coupled to aphotodiode strip array). The spatial resolution of a basic edge-onplanar detector along the dimension of the aperture is defined by thethickness of the edge unless a collimator is used to restrict theincident radiation along that dimension. Increased spatial resolutionrequires the use of thinner planar detectors. The number of detectorplanes (and readout elements) doubles each time the aperture height ishalved (the aperture resolution doubles). This forces an increase in thepacking density of electronics that resides near the array of basicedge-on detectors. As the number of basic edge-on detectors per detectormodule increases so does the inactive volume (dead space) due to thethickness of the photodetector readout (for edge-on scintillatordetectors) and any gaps between the basic edge-on detectors. The problemof dead space between basic edge-on detector planes is more severe forbasic edge-on scintillator array detectors than for basic edge-onsemiconductor array detectors. For example, deploying a basic edge-onscintillator detector design for a high resolution PET detector requiresa very large number of very thin photodetectors such as Geiger-modesilicon photomultiplier (SiPM) arrays, internal discrete amplificationphotodetector arrays, avalanche photodiode (APD) linear arrays orposition-sensitive APDs (PSAPDs) optically coupled to 1-D arrays of LSOscintillator rods with a 1 mm aperture height; see, e.g., Levin (2004)Nuc. Instr. Meth. Phys. Res. A 527:35-40; Levin (2004) IEEE Trans. Nucl.Sci. Vol. 51, No. 3, pp. 805-810, June 2004.

Although these readout detectors are expected to have a thickness lessthan 0.5 mm this thickness (dead space) is non-negligible compared tothe 1 mm aperture height (and it is still significant even for a 3 mmaperture height) of the LSO scintillator array. This dead space degradesthe spatial resolution in one dimension as well as the detectionefficiency. The impact of this dead space could be mitigated if thescintillator rod aperture height was much larger. (A significantincrease in aperture height would ease the requirements on the thickness(and cost) of the readout detector. The readout detector thickness wouldonly need to be sufficiently thin so that the impact of dead spaces or“gaps” between basic edge-on scintillator detectors or edge-onscintillator detector modules on spatial resolution and detectionefficiency is acceptable for the imaging task. Commercial, face-onmodular gamma cameras have gaps between the butted detector modules.)Another application that benefits from a thin photodetector readoutdetector is a face-on, wearable PET detector for small animal brainimaging that uses wafer-thin APD arrays, Vaska P, et al., IEEE Trans.Nucl. Sci. Vol. 51, No. 5, pp. 2718-2722, October 2004.

The number of basic edge-on scintillator or semiconductor detectorplanes required to assemble an edge-on detector module can be reduced byimplementing the techniques developed for measuring the “depth ofinteraction” (DOI) within face-on scintillator and semiconductordetectors. The benefits of this approach can be illustrated byconsidering a scenario in which radiation is incident face-on upon theanode or cathode side of a planar semiconductor detector of known depthor thickness (height). The DOI spatial resolution can be determined bymeasuring either the transit times of electrons and holes to anodes andcathodes, respectively, or the ratio of anode and cathode signals. Thesemiconductor detector DOI accuracy is affected by parameters such asthe detector depth, electron and hole mobility, signal diffusion, andthe number of defects (such as traps) in the bulk semiconductormaterial. (The specific parameters that affect scintillator detector DOIaccuracy vary with the DOI measurement technique.) Orient the planarsemiconductor detector edge-on to the source of incident radiation. Theplanar semiconductor detector thickness now defines the maximum heightof the edge-on semiconductor detector entrance aperture. Theelectronically-measured face-on detector DOI positional information nowdefines the edge-on detector sub-aperture resolution (SAR). Theinteraction position along the height of the edge-on detector apertureis referred to as the interaction height.

SUMMARY OF THE INVENTION

The invention provides edge-on SAR scintillator detector designs andsystems for enhanced SPECT, PET, and Compton gamma cameras, which can beemployed in any appropriate system, e.g., for medical diagnosis. In oneaspect, the invention provides edge-on SAR scintillator detector designsand systems for enhanced SPECT, PET, and Compton gamma cameras employedin nuclear medicine. In one aspect, the devices of the present inventionare implementations of edge-on scintillator elements (rods, blocks)coupled to photodetector readout arrays with SAR capability that aresuitable for constructing edge-on SAR scintillator detector modules foruse in enhanced edge-on SPECT, PET, and Compton gamma cameras, as wellas hand-held SPECT and PET cameras, e.g., for use in nuclear medicine.Additional applications include (photon, particle) radiation therapyportal imaging, nuclear remediation, mine detection, containerinspection, and high energy physics and astronomy (x-rays, gamma rays,particles).

This invention provides edge-on SAR scintillator rod detector modulewherein at least one encoding technique is employed comprising modifyinga rod surface, introducing internal structures into a rod, structuredlight sharing between rods, and employing rods or rod segments withdifferent pulse properties. In one aspect, a rod surface is modified byemploying at least one surface treatment from: surface roughness,surface cuts, reflectors, absorbers, WLS materials, IOR differences, IORgradients, and/or coupling structures. In one aspect, a rod interior ismodified by employing at least one of: segments, sub-rods, continuousboreholes, partial boreholes. In one aspect, rod structured lightsharing is implemented by employing at least one of: shared windows,offset rod segments.

In one aspect, rod pulse properties comprise at least one of: pulseshape, color spectrum. In one aspect, the surface of a rod segment ismodified using surface treatment techniques. In one aspect, theboreholes comprise physical and virtual boreholes. In one aspect,physical borehole modifications comprise at least one of shape, surfacetreatment, and internal structure. In one aspect, aligned boreholes inadjacent layers are connected and provide SAR information. In oneaspect, sub-rods are modified using at least one of surface treatmenttechniques, internal structure techniques, structured light sharingtechniques. In one aspect, the rod shared window technique defines acell. In one aspect, the rod shared window technique employs asymmetric1-D windows.

In one aspect, the rod shared window technique employs alternatinglayers of cross-coupled optical fibers and rods. In one aspect, the rodshared window technique employs alternating layers of cross-coupledcells. In one aspect, the rod shared window technique employsalternating layers of cross-coupled fibers and rods. In one aspect, rodsegments are offset either within a single layer or within a singlelayer and between adjacent layers. In one aspect, offset rod segmentsuse different materials. In one aspect, the offset rod segments aremodified using at least one of surface treatment techniques, internalstructure techniques, and structured light sharing techniques. In oneaspect, multiple materials are layered.

The invention provides a multi-material edge-on SAR scintillatordetector module of the invention wherein multiple materials are deployedwithin the same layer. In one aspect, either a one-side readout or amultiple-side readout is employed.

The invention provides edge-on SAR scintillator block detector moduleswherein at least one encoding technique is employed comprising modifyinga block surface, introducing internal structures into a block,structured light sharing between blocks, and employing blocks withdifferent pulse properties. In one aspect, the surface is modified byemploying at least one surface treatment from: surface roughness,surface cuts, reflectors, absorbers, WLS materials, IOR differences, IORgradients. In one aspect, the scintillator block is a narrow, 2-D SARscintillator sheet. In one aspect, the interior is modified by employingat least one of: sub-sheets, continuous boreholes, and partialboreholes. In one aspect, structured light sharing is implemented byemploying shared windows. In one aspect, pulse properties include atleast one of: pulse shape, color spectrum. In one aspect, boreholesinclude physical and virtual boreholes. In one aspect, physical boreholemodifications include at least one of shape, surface treatment, andinternal structure. In one aspect, sub-sheets are modified using atleast one of surface treatment techniques, internal structuretechniques, structured light sharing techniques. In one aspect, either aone-side readout or a multiple-side readout is employed. In one aspect,aligned boreholes in adjacent layers are connected and provide SARinformation. In one aspect, a modular, edge-on scintillator ringdetector is used. In one aspect, either axial-on SAR scintillatordetector modules or basic edge-on scintillator detector modules areemployed. In one aspect, scintillator rod ends have either a uniformrectangular geometry or an annular geometry cross-section. In oneaspect, scintillator block ends have either a uniform rectangulargeometry or an annular geometry cross-section. In one aspect, axialedge-on SAR scintillator detector modules are employed. In one aspect,the scintillator rods are assembled in a uniform rectangular geometry ora wedge geometry. In one aspect, the scintillator blocks are assembledin a uniform rectangular geometry or a wedge geometry.

The invention provides segmented readout photodetectors for edge-on andface-on scintillator detector modules. In one aspect, photodetectorcomprises one of: a strip array PSAPD detector, a sub-strip array PSAPDdetector, a sub-area array PSAPD detector, a mixed PSAPD detector,and/or a sub-strip SDD detector. These readout geometries can beimplemented using SiPM arrays or internal discrete amplificationphotodetector arrays. These segmented readout photodetectors can beincorporated into, or used with, any edge-on scintillator detectormodule device of the invention.

In accordance with the present invention, an edge-on scintillatordetector module with SAR capability is provided as a radiation detectiondevice for nuclear medicine (SPECT, PET, Compton camera) imaging.Specific implementations can be used for SPECT-PET imaging and hand-heldSPECT or PET camera imaging, including probes. The edge-on SARscintillator detector module can be used to detect both particle andphoton radiation, making it suitable for other applications such asradiation therapy portal imaging, nuclear remediation, mine detection,container inspection, and high energy physics and astronomy. Two mainimplementations of the edge-on SAR scintillator detector module useeither scintillator rods or scintillator blocks. Two categories ofscintillator blocks include 3-D and 2-D (sheet) blocks. Trade-offs existin terms of cost of implementation, spatial and energy resolution,response uniformity, dead detector volume, and detector dead time.Scintillator rods and blocks can both be incorporated into an edge-onSAR scintillator detector module. A number of external (surface) andinternal optimization techniques (encoding methods) are described thatcan result in improved SAR resolution. Multiple scintillator materialsas well as non-scintillator materials can be incorporated into anedge-on SAR scintillator detector module. A variety of photodetectorreadout systems can be coupled to an edge-on SAR scintillator detectormodule. Two exemplary readout formats are one-side and multi-side(typically two-side) readout. Exemplary photodetector geometries include2-D arrays, 1-D strip arrays, and position-sensitive area detectors.Modifications to these photodetector geometries may reduce photodetectorreadout noise as well as edge-on SAR scintillator detector dead time.Thin photodetector devices can be used to minimize the dead spacebetween detector modules.

The invention provides products of manufacture, or apparatus, fordetecting radiation comprising: an edge-on sub-aperture resolution (SAR)scintillator rod detector module of the invention; a multi-materialedge-on SAR scintillator detector of the invention; an edge-on SARscintillator block detector module of the invention; an axial-on SARscintillator detector module of the invention; or a segmented readoutphotodetector for edge-on and face-on scintillator detector modules ofthe invention; or any combination thereof. In one aspect, the productsof manufacture, or apparatus, are used to detect radiation, for example,the detected radiation can be x-ray, beta radiation, gamma ray, and/orparticle radiation. In one aspect, the products of manufacture, orapparatus, comprise a SPECT device, a PET device, a Compton probedetector or a Compton camera, or a combination thereof. In one aspect,the products of manufacture, or apparatus, can be hand-held devices.

The invention provides container inspection device for detectingradiation comprising: an edge-on sub-aperture resolution (SAR)scintillator rod detector module of the invention; a multi-materialedge-on SAR scintillator detector of the invention; an edge-on SARscintillator block detector module of the invention; an axial-on SARscintillator detector module of the invention; or a segmented readoutphotodetector for edge-on and face-on scintillator detector modules ofthe invention; or any combination thereof. In one aspect, the productsof manufacture, or apparatus, are used to detect radiation, for example,the detected radiation can be x-ray, beta radiation, gamma ray, and/orparticle radiation. In one aspect, the container inspection devicefurther comprises, is part of, or is operably linked to a SPECT device,a PET device, a Compton probe detector, a Compton camera, or acombination thereof. In one aspect, the container inspection device is ahand-held device.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a two-side readout using perpendicular stripphotodetectors as set forth in FIG 1. The invention provides products ofmanufacture, or apparatus, including, e.g., edge-on sub-apertureresolution (SAR) scintillator rod detector modules, comprising anedge-on scintillator rod with an internal structure consisting ofmultiple segments as set forth in FIG 2 c. The invention providesproducts of manufacture, or apparatus, including, e.g., edge-onsub-aperture resolution (SAR) scintillator rod detector modules,comprising an edge-on scintillator rod with an internal structureconsisting of a single modified segment with a surface treatmentcomprised of a reflective grid pattern as set forth in FIG 2 d. Theinvention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising an edge-on scintillator rod with an internalstructure consisting of a single modified segment with a surfacetreatment comprised of a focused pattern of shallow surface cuts as setforth in FIG 2 e. The invention provides products of manufacture, orapparatus, including, e.g., edge-on sub-aperture resolution (SAR)scintillator rod detector modules, comprising an edge-on scintillatorrod with an internal structure consisting of an array of boreholes asset forth in FIG 2 f. The invention provides products of manufacture, orapparatus, including, e.g., edge-on sub-aperture resolution (SAR)scintillator rod detector modules, comprising an edge-on scintillatorrod with an internal structure consisting of 1-D and 2-D sub-rods as setforth in FIG 2 g.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a 2-rod cell wherein a 1-D shared window (a 1-Dwindow pattern) couples a scintillator rod to one adjacent scintillatorrod as set forth in FIG 3 a. The invention provides products ofmanufacture, or apparatus, including, e.g., edge-on sub-apertureresolution (SAR) scintillator rod detector modules, comprising a 4-rodcell wherein a scintillator rod with a 2-D shared window (lower rightcorner) is coupled to two adjacent scintillator rods as set forth in FIG3 b, and optionally the 2-D shared window comprising two asymmetric 1-Dwindow patterns.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a shared window defined by cross-coupling twoedge-on scintillator rod arrays as set forth in FIG 4 a. The inventionprovides products of manufacture, or apparatus, including, e.g., edge-onsub-aperture resolution (SAR) scintillator rod detector modules,comprising a shared window defined by cross-coupling two edge-onscintillator rod arrays as set forth in FIG 4 b.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a single layer of offset edge-on scintillator rodsegments as set forth in FIG 5 a. The invention provides products ofmanufacture, or apparatus, including, e.g., edge-on sub-apertureresolution (SAR) scintillator rod detector modules, comprising a 2-layercell of offset edge-on scintillator rod segments in which segments areoffset within a layer and between layers as set forth in FIG 5 b.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a stack of edge-on scintillator blocks comprisingscintillator materials with single-side readouts as set forth in FIG 6.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising horizontal and vertical stacks of edge-onscintillator sheets as set forth in FIG 7.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising horizontal edge-on scintillator sheets with aninternal structure comprising an array of boreholes as set forth in FIG8.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a horizontal stack of edge-on scintillator sheetswith an internal structure comprising an array of coupled boreholes withfiber optics as set forth in FIG 9.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a strip array PSAPD wherein each strip is providedwith dual readout electrodes (a SA-PSAPD) as set forth in FIG 10 a. Theinvention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising a strip array PSAPD wherein each strip is dividedinto multiple sub-strips and each sub-strip is provided with dualreadout electrodes (a SSA-PSAPD) as set forth in FIG 10 b.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, comprising an axial edge-on SAR scintillator ring PET detectorconfiguration with a uniform rectangular geometry as set forth in FIG 11a. The invention provides products of manufacture, or apparatus,including, e.g., edge-on sub-aperture resolution (SAR) scintillator roddetector modules, comprising axial-on SAR scintillator rods with anannular cross section that increases with radius suitable for a ring PETdetector configuration as set forth in FIG 11 b. The invention providesproducts of manufacture, or apparatus, including, e.g., edge-onsub-aperture resolution (SAR) scintillator rod detector modules,comprising an axial edge-on SAR scintillator ring PET detectorconfiguration with a truncated-triangle (wedge) geometry as set forth inFIG 11 c.

The invention provides products of manufacture, or apparatus, including,e.g., edge-on sub-aperture resolution (SAR) scintillator rod detectormodules, edge-on sub-aperture resolution (SAR) scintillator rod detectormodule comprising at least any two of the structural limitations setforth herein, e.g., in FIGS. 1 to 11.

The invention provides edge-on imaging probe detectors, wherein at leastone detector type is employed from: an edge-on scintillator detectorand, an edge-on semiconductor detector. In one aspect, the inventionprovides edge-on imaging probe detectors comprising at least onedetector type selected from the group consisting of an edge-onscintillator detector, an edge-on semiconductor detector and acombination thereof. The invention provides products of manufacture, orapparatus, comprising these edge-on imaging probe detectors. In oneaspect, the edge-on imaging probe detectors are used in nuclearmedicine, e.g., for radiation therapy portal imaging, or for use innuclear remediation, mine detection, container inspection, and highenergy physics and astronomy. The invention provides single photonemission computed tomography (SPECT) devices, positron emissiontomography (PET) devices or Compton gamma cameras comprising the edge-onimaging probe detector of the invention. In one aspect, an apparatus ofthe invention further comprises, is operably linked to, or is part of asingle photon emission computed tomography (SPECT) device, a positronemission tomography (PET) device, a Compton probe detector or a Comptongamma camera

In one aspect, in the edge-on imaging probe detectors of the invention,the edge-on scintillator detector implements at least one of: a rodgeometry, and/or a block geometry, or a combination thereof. In oneaspect, the edge-on imaging probe detector has a detector geometrycomprising, e.g., a basic edge-on detector, an enhanced edge-on detectoror a combination thereof. In one aspect; the detector geometry comprisesa mixed edge-on detector, an enhanced edge-on detector, a basic edge-ondetector, a hybrid edge-on detector or a combination thereof. In oneaspect, the detector geometry comprises hybrid edge-on detectors.

In one aspect, the detector generates a readout element pitch, whereinoptionally the readout element pitch is variable. In one aspect, thedetector generates a horizontal readout strip pitch, wherein optionallythe horizontal readout strip pitch is variable. In one aspect, thedetector generates a segmented readout strip pitch wherein optionallythe segmented readout strip pitch is variable along a verticaldirection. In one aspect, at least one of the edge-on imaging probedetectors is configured in a 4-quadrant geometry. In one aspect, atleast one of the edge-on imaging probe detectors is configured in a4-quadrant geometry and comprises an internal collimator. In one aspect,the edge-on imaging probe detector comprises a limited, basic 2-Dedge-on detector.

In one aspect, the edge-on imaging probe detector of the inventionfurther comprises, or is operably linked to, or is part of an edge-onsub-aperture resolution (SAR) scintillator rod detector, a single photonemission computed tomography (SPECT) device, a positron emissiontomography (PET) device, a Compton probe detector or a Compton gammacamera. In one aspect, the SAR edge-on detector is a limited, 3-D SARedge-on detector. In one aspect, the edge-on detector is configured as aCompton probe detector, a dual-detector probe or a combination thereof.

The invention provides a mine detection probe operably linked to theedge-on imaging probe detector of the invention, or comprising theedge-on imaging probe detector of the invention.

The invention provides a radiation detection device operably linked tothe edge-on imaging probe detector of the invention, or comprising theedge-on imaging probe detector of the invention.

In one aspect of the edge-on imaging probe detector of the invention,the edge-on imaging probe detector comprises non-detector materials. Inone aspect, the edge-on imaging probe detector comprises (implements) anelectronic internal collimator.

The invention provides a method of providing electronic internalcollimation by selectively ignoring specific patterns of detectorelements either by not reading them or by reading them and not includingtheir data during image reconstruction.

In one aspect, the invention provides novel edge-on imaging probedetector designs for medical imaging purposes, e.g., for nuclearmedicine, e.g., for experimental, diagnostic or treatment purposes. Inone aspect, the devices of the invention are implementations of 1-D and2-D arrays of basic edge-on semiconductor detector elements orscintillator detector elements, which in alternative aspects lack SARcapabilities. These embodiments are referred to as “basic” edge-onimaging probe detector designs. Detector elements of the invention cantake the form of strips or pixels.

In one aspect, the devices of the present invention are implementationsof 2-D and 3-D arrays of SAR edge-on semiconductor detector elements orscintillator detector elements. These embodiments are referred to as“enhanced” or SAR edge-on imaging probe detector designs. In one aspect,the devices of the present invention are implementations of both basicand SAR edge-on semiconductor detector arrays or scintillator detectorarrays. These are referred to as “mixed” edge-on imaging probe designs.

In one aspect, the devices of the present invention are implementationsof basic and (or) SAR edge-on semiconductor detector arrays and (or)scintillator detector arrays layered with face-on semiconductor orscintillator detector arrays. These embodiments are referred to as“hybrid” edge-on imaging probe detector designs. Edge-on detector arrayscan be stacked (layered) in basic, enhanced, mixed, and/or hybridedge-on imaging probe designs. Basic and/or SAR edge-on detector canutilize multiple materials. Edge-on imaging probe designs mayincorporate internal collimators, external collimators, both internaland/or external collimators, or none at all. Edge-on imaging probedetector designs are suitable for imaging charged or neutral particles,coincident photons, and/or non-coincident photons.

The invention provides 1-D edge-on semiconductor detectors assembled asa 2-D edge-on imaging probe detector comprising an edge-on imaging probedetector of the invention. In one aspect, the 1-D edge-on semiconductordetector is configured as set forth in FIG 12 a.

The invention provides arrays of basic, 1-D edge-on semiconductordetectors assembled as a 4-quadrant edge-on imaging probe detectorconfigured as set forth in FIG 12 b. In one aspect, these 1-D edge-onsemiconductor detectors comprise at least one internal collimator. Inone aspect, these 1-D edge-on semiconductor detectors comprise anedge-on imaging probe detector of the invention.

The invention provides butted pair of basic, 1-D edge-on semiconductordetectors comprising variable anode strip pitch near the radiationentrance surface for use in a 4-quadrant edge-on imaging probe detectorof the invention. In one aspect, these butted pair of basic, 1-D edge-onsemiconductor detectors are configured as set forth in FIG 13 a. In oneaspect, these basic, 1-D edge-on semiconductor detectors comprise anedge-on imaging probe detector of the invention.

The invention provides arrays of limited, basic, 2-D edge-onsemiconductor detectors with a segmented anode strip and a variableanode strip pitch along the vertical direction near the entrancesurface, comprising the edge-on imaging probe detector of the invention.In one aspect, these 2-D edge-on semiconductor detectors are configuredas set forth in FIG 13 b.

The invention provides arrays of limited, basic, 2-D edge-onsemiconductor detectors with anode strips and crossed cathode stripswith a variable cathode strip pitch near the entrance surface,comprising the edge-on imaging probe detector of the invention. In oneaspect, these basic, 2-D edge-on semiconductor detectors are configuredas set forth in FIG 13 b.

The invention provides enhanced 3-D edge-on imaging probe detectorscomprising a SAR edge-on scintillator rod array in which the first layerof scintillator rods can be thin (a variable rod pitch along thevertical direction near the entrance surface) and of a materialcomprising a plastic scintillator or a low Z scintillator crystal inorder to image charge particles or low energy gamma rays. In one aspect,these enhanced 3-D edge-on imaging probe detectors are configured as setforth in FIG 14. In one aspect, these enhanced 3-D edge-on imaging probedetectors comprise the edge-on imaging probe detector of the invention.

The invention provides mixed edge-on imaging probe detectors comprisinga single layer SAR scintillator rod array comprising a plasticscintillator or a low Z scintillator crystal material for imaging chargeparticles or a low energy gamma rays stacked on top of an array ofbasic, and 1-D edge-on semiconductor detectors assembled as a 4-quadrantedge-on detector with an internal collimator. In one aspect, these mixededge-on imaging probe detectors comprise the edge-on imaging probedetector of the invention. In one aspect, these mixed edge-on imagingprobe detectors are configured as set forth in FIG 15.

The invention provides hybrid imaging probe detectors comprising a thin,2-D, face-on silicon (Si) array detector for charge particle that isstacked on top of a 4-quadrant edge-on semiconductor detector array withan internal collimator. In one aspect, these hybrid imaging probedetectors comprise a face-on detector array comprising a plasticscintillator or a low Z phosphor material coupled to a thinnedphotodetector array. In one aspect, these hybrid imaging probe detectorsare configured as set forth in FIG 16. In one aspect, these hybridimaging probe detectors comprise the edge-on imaging probe detector ofthe invention.

In one aspect, the invention provides edge-on sub-aperture resolution(SAR) scintillator devices, detectors, designs and systems comprisingthe hybrid imaging probe detectors of the invention, or the mixededge-on imaging probe detectors of the invention, or the enhanced 3-Dedge-on imaging probe detectors of the invention, or arrays of limited,basic, 2-D edge-on semiconductor detectors of the invention, or thebutted pair of basic, 1-D edge-on semiconductor detectors of theinvention, or the 1-D edge-on semiconductor detectors assembled as a 2-Dedge-on imaging probe detector of the invention, or the 2-D and 3-Darrays of SAR edge-on semiconductor detector elements or scintillatordetector elements of the invention, or a combination thereof. Inalternative aspects, these detection devices can be used to detect anyform of radiation for, e.g., medical purposes, or industrial, homelandsecurity or defense purposes, e.g., to detect radiation in mines, ships,shipping containers, airplanes, packages, cars, trucks and the like. Inone aspect, the detection devices, detectors, designs and/or systems arehandheld devices.

The invention provides silicon drift detector (SDD), a photodiode array,a Geiger-mode silicon photomultiplier (SiPM) array, an internal discreteamplification photodetector array, an APD array or a position-sensitiveAPD (PSAPD) comprising the edge-on imaging probe detector of theinvention.

The invention provides silicon drift detector (SDD), a photodiode array,a Geiger-mode silicon photomultiplier (SiPM) array, an internal discreteamplification photodetector array, an APD array or a position-sensitiveAPD (PSAPD) comprising the hybrid imaging probe detectors of theinvention, or the mixed edge-on imaging probe detectors of theinvention, or the enhanced 3-D edge-on imaging probe detectors of theinvention, or arrays of limited, basic, 2-D edge-on semiconductordetectors of the invention, or the butted pair of basic, 1-D edge-onsemiconductor detectors of the invention, or the 1-D edge-onsemiconductor detectors assembled as a 2-D edge-on imaging probedetector of the invention, or the 2-D and 3-D arrays of SAR edge-onsemiconductor detector elements or scintillator detector elements of theinvention, or a combination thereof.

The compositions, devices, detectors, designs and systems of theinvention can be used with any known device, e.g., with any knownimaging device, e.g., as an integral part of the device or operativelylinked to the device; for example, compositions, devices, detectors,designs and systems of the invention can be used with any known enhancedsingle photon emission computed tomography (SPECT) device or system, orany known positron emission tomography (PET) device or system, or anyknown gamma camera, e.g., a Compton gamma camera, any known X-rayimaging, any known fluoroscopy device or system, or any known computedtomography (CT) device or system, or any known digital mammographydevice or system, or any known magnetic resonance imaging (MRI) deviceor system, or any known ultrasound device or system; as described, e.g.,in U.S. Pat. Nos. 7,019,297; 6,996,430; 6,992,762; 6,967,331; 6,978,039;6,943,355; 6,921,840; 6,917,826; 6,803,580; 6,794,653; 6,774,358;6,558,333; 6,642,523; 6,429,434; 6,289,235; 6,226,543.

These and other advantages of the present invention will become apparentupon reference to the accompanying drawings and the followingdescription.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

All publications, patents, patent applications, U.S. Patent OfficeDisclosure Documents, cited herein are hereby expressly incorporated byreference for all purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of edge-on SAR scintillator roddetector module with a two-side readout using perpendicular stripphotodetectors.

FIG. 2 a illustrates a perspective view of a surface treatment comprisedof absorptive black stripes distributed along the surface of an edge-onscintillator rod.

FIG. 2 b illustrates a perspective view of a surface treatment comprisedof angled surface cuts distributed along a surface of an edge-onscintillator rod.

FIG. 2 c illustrates a perspective view of an edge-on scintillator rodwith an internal structure consisting of multiple segments.

FIG. 2 d illustrates a perspective view of an edge-on scintillator rodwith an internal structure consisting of a single modified segment witha surface treatment comprised of a reflective grid pattern.

FIG. 2 e illustrates a perspective view of an edge-on scintillator rodwith an internal structure consisting of a single modified segment witha surface treatment comprised of a focused pattern of shallow surfacecuts.

FIG. 2 f illustrates a perspective view of an edge-on scintillator rodwith an internal structure consisting of an array of boreholes.

FIGS. 2 g-2 h illustrates perspective views of an edge-on scintillatorrod with an internal structure consisting of 1-D and 2-D sub-rods.

FIG. 3 a illustrates a perspective view of a 2-rod cell wherein a 1-Dshared window (a 1-D window pattern) couples a scintillator rod to oneadjacent scintillator rod.

FIG. 3 b illustrates a perspective view of a 4-rod cell wherein ascintillator rod with a 2-D shared window (lower right corner) iscoupled to two adjacent scintillator rods. (The second scintillator rodwith a 2-D shared window in the upper left corner is omitted forclarity.) The 2-D shared window is comprised of two asymmetric (offset),1-D window patterns is shown.

FIG. 4 a illustrates a perspective view of a shared window defined bycross-coupling two edge-on scintillator rod arrays.

FIG. 4 b illustrates a perspective view of shared window defined bycross-coupling a fiber array and an edge-on scintillator rod array.

FIG. 5 a illustrates a perspective view of a single layer of offsetedge-on scintillator rod segments.

FIG. 5 b illustrates a perspective view of a 2-layer cell of offsetedge-on scintillator rod segments in which segments are offset within alayer and between layers.

FIG. 6 illustrates a perspective view of a stack of edge-on scintillatorblocks 1-3 comprised of scintillator materials 1-3 with single-sidereadouts.

FIG. 7 illustrates perspective views of horizontal and vertical stacksof edge-on scintillator sheet.

FIG. 8 illustrates a perspective view of a horizontal edge-onscintillator sheet with an internal structure consisting of an array ofboreholes.

FIG. 9 illustrates a perspective view of a horizontal stack of edge-onscintillator sheet with an internal structure consisting of an array ofcoupled boreholes with fiber optics.

FIG. 10 a illustrates a perspective view of a strip array PSAPD whereineach strip is provided with dual readout electrodes (a SA-PSAPD).

FIG. 10 b illustrates a perspective view of a strip array PSAPD whereineach strip is divided into multiple sub-strips and each sub-strip isprovided with dual readout electrodes (a SSA-PSAPD).

FIG. 11 a illustrates a perspective view of an axial edge-on SARscintillator ring PET detector configuration with a uniform rectangulargeometry.

FIG. 11 b illustrates a perspective view of axial-on SAR scintillatorrods with an annular cross section that increases with radius suitablefor a ring PET detector configuration.

FIG. 11 c illustrates a perspective view of an axial edge-on SARscintillator ring PET detector configuration with a truncated-triangle(wedge) geometry.

FIG. 12 a illustrates a perspective view of an array of basic, 1-Dedge-on semiconductor detectors assembled as a 2-D edge-on imaging probedetector.

FIG. 12 b illustrates a perspective view of an array of basic, 1-Dedge-on semiconductor detectors assembled as a 4-quadrant edge-onimaging probe detector with internal collimator (not shown for clarity).

FIG. 13 a illustrates a perspective view of a butted pair of basic, 1-Dedge-on semiconductor detectors with variable anode strip pitch near theradiation entrance surface suitable for use in a 4-quadrant edge-onimaging probe detector.

FIG. 13 b illustrates a perspective view of an array of limited, basic,2-D edge-on semiconductor detector with a segmented anode strip(variable anode strip pitch along the vertical direction near theentrance surface).

FIG. 13 c illustrates a perspective view of an array of limited, basic,2-D edge-on semiconductor detector with anode strips and crossed cathodestrips with a variable cathode strip pitch near the entrance surface.

FIG. 14 illustrates a perspective view of an enhanced (SAR), 3-D edge-onimaging probe detector comprised of a SAR edge-on scintillator rod arrayin which the first layer of scintillator rods can be thin (a variablerod pitch along the vertical direction near the entrance surface) and ofa material such as a plastic scintillator or low Z scintillator crystalin order to image charge particles or low energy gamma rays.

FIG. 15 illustrates a perspective view of a mixed edge-on imaging probedetector comprised of a single layer SAR scintillator rod array of aplastic scintillator or low Z scintillator crystal material for imagingcharge particles or low energy gamma rays stacked on top of an array ofbasic, 1-D edge-on semiconductor detectors assembled as a 4-quadrantedge-on detector with an internal collimator.

FIG. 16 illustrates a perspective view of a hybrid imaging probedetector comprised of a relatively thin, 2-D, face-on Si array detectorfor charge particle that is stacked on top of a 4-quadrant edge-onsemiconductor detector array with an internal collimator (collimator notshown). A variant of this design uses a face-on detector array comprisedof a plastic scintillator or low Z phosphor material coupled to athinned photodetector array.

DETAILED DESCRIPTION

The invention provides designs for edge-on scintillator rod and blockdetectors with SAR capability, as well as readout devices, which areincorporated into discrete detector modules that can be used forradiation imaging directly, for small hand-held imaging devices, and/oras part of a detector module array. Edge-on SAR scintillator rod andblock detectors typically implement one-side or two-side readoutdesigns. Planar and ring detector geometries are widely used in nuclearmedicine. Arrays of edge-on SAR detector modules can be assembled toform planar and ring detectors. The general properties of an edge-ondetector module (comprised of edge-on scintillator and semiconductordetectors, readout and processing electronics, power management,communications, temperature control, and radiation shielding) as well asseveral edge-on detector module array configurations are described inNelson, U.S. Pat. No. 6,583,420 and Nelson, U.S. Pat. Appl. publicationNo. 20040251419, and Nelson, U.S. Patent Office Disclosure Document No.567471. Specific 1-D and 2-D edge-on scintillator and semiconductordetectors (including DOI capability) without SAR capabilities aredescribed in Nelson, U.S. Pat. No. 4,560,882 and Nelson, U.S. Pat. No.4,937,453. Efficient manufacturing techniques to build structured 1-Dand 2-D scintillator arrays for gamma and x-ray detection are describedin Nelson, U.S. Pat. No. 5,258,145.

In some aspects, the invention's use of edge-on detector with SARcapability can significantly lower the cost of deploying edge-ondetectors in nuclear medicine imaging systems. There are a number ofbenefits associated with implementing SAR capabilities in edge-ondetectors. The edge-on detector aperture height no longer limits theaperture spatial resolution. The total number of basic edge-on detectorsand the number of readout channels (readout electronics) required tocover a desired imaging area is reduced. The sub-aperture positionalinformation may allow meaningful corrections to the expected signallosses and thus improve energy resolution. Other benefits can include anincrease in available image detector volume due to a decrease in thenumber of edge-on detector physical boundaries (detector materialproperties typically degrade near the perimeter) and the number of gapsthat may be present between edge-on detector planes. Limitations mayinclude the need for better timing resolution, additional (and faster)signal processing, and a decrease in the event count rate. Edge-onSPECT, PET, and Compton gamma cameras that utilize edge-on detectorswith SAR capabilities are referred to as “enhanced” edge-on SPECT, PET,and Compton gamma cameras, respectively.

Consider a specific example of a detector module that might be used forface-on, high resolution PET imaging. Suppose that a face-on detectormodule that consists of a 30×30 array of 1×1×10 mm³ scintillator rods(approximately 10 mm of stopping power using BGO, LSO, YAP, etc.scintillator material) uses a two-side or dual readout design. Theface-on detector surface resolution is 1×1 mm² (ignoring the thicknessof any reflective coating or gaps that are present). Suppose that theface-on DOI resolution is approximately 1 mm FWHM. Now turn the face-onarray on its side or “edge-on” (FIG 1). The stopping power is nowincreased from 10 mm to 30 mm although the surface area of the detectorface is now reduced from 30×30 mm² to 30×10 mm². The edge-onscintillator detector DOI resolution is now fixed by the dimension of ascintillator rod element at 1 mm (eliminating signal strengthdepth-dependence). The edge-on detector surface resolution is now 1mm×the aperture resolution (which was determined electronically to be 1mm based on the face-on DOI measurement).

A problem with face-on DOI scintillator detectors is that Comptonscattering of incident radiation is biased in the forward direction suchthat the probability of detecting the scatter event downstream from theinitial off-axis event within the same scintillator rod may not be small(resulting in an inaccurate DOI estimate). The edge-on SAR scintillatorrod detector design reduces the likelihood that a Compton scatter photonwill be detected in the same scintillator rod for a relatively largerange of incident angles. This simplifies the tracking of mostsubsequent interactions or events after a primary interaction.

The edge-on SAR scintillator detector module format may reduce the costof using certain scintillator materials as well as the readoutdetectors. Scintillator rods with smaller lengths may have superiormanufacturing yields. Furthermore, if the required DOI resolution is 3mm rather than 1 mm the scintillator rod dimensions can be relaxed to1×3×10 mm³, reducing the number of rods by ⅓ and lowering manufacturingcosts even more. (Note that this benefit needs to be balanced againstthe increased probability of a Compton event within the same rod with alateral offset.) Providing 1 mm aperture resolution over 10 mm is nowaccomplished with 2 readout arrays rather than 10 readout arraysindividually-coupled to a basic edge-on scintillator array with 1 mmaperture height. The total lost detector volume due to the thickness ofthe readout arrays is also reduced by (approximately) a factor of 5.(Note that the energy resolution of a dual readout, edge-on SARscintillator rod design is likely to be reduced compared to a basicedge-on scintillator detector design.)

An alternative to the edge-on SAR scintillator rod design is the edge-onscintillator block (3-D block or 2-D sheet). Several factors willinfluence the decision to use edge-on SAR scintillator rods or blocks(or both) in detector modules. The block design could lower the cost ofthe scintillator elements since it typically requires fewer scintillatorelements than rod designs. Certain block designs will experience anincrease in signal noise due to the detection of a greater number ofCompton scatter events. The use of scintillator blocks rather than rods,due to the increased scintillator volume, will increase the over-alldetector module dead time per unit volume. The response uniformity of ablock may worsen near or away from certain boundaries depending on itsdimensions and surface modifications. Detector modules based on edge-onSAR scintillator rods (depending on the design) may offer more uniformspatial resolution and better energy resolution than detector modulesbased on edge-on SAR scintillator blocks but at a greater cost.

Two types of exemplary edge-on scintillator rod configurations, singlerod geometries and structured light sharing rod geometries, for edge-onSAR scintillator rod detector modules will be described. A number ofoptimization techniques (such as the use of internal structures, surfacetreatments, and pulse properties (pulse shape, color)) may be applied.The choice of configuration and optimization technique(s) for a SPECT orPET edge-on SAR scintillator detector module will be the result ofnumerous trade-offs: desired spatial resolution and uniformity, energyresolution, pulse properties (pulse shape, spectrum), scintillator IOR,energy-dependent conversion efficiency, stopping power, the energyrange, the photodetector readout, the count rate, and the imaginggeometry (planar or ring, large or small volume).

Single Rod Geometries.

Scintillator rod 202 geometries can benefit from the application ofsurface modification techniques (FIGS. 2 a-2 b). Uniform and non-uniform(patterned) surface treatments include modifying absorption 203,reflection, IOR mismatches, IOR gradients, spectral properties (usingwavelength shifting (WLS) materials), and scattering properties as afunction of position by applying coatings, controlling surfaceroughness, introducing shallow surface cuts 204, and applying couplingstructures such as very thin focused fiber bundle layers or SELFOCmicrolenses. For example, diffuse or specular reflective coatings, films(or reflective sheets) are often used to provide optical isolationbetween layers of scintillator rods (allowing optical communicationwithin a layer) or between adjacent scintillator rods. A WLS materialcan provide additional encoded information if the readout deviceprovides a color-sensitive response (due to the use of a color filter orthe inherent spectral response of the photodetector) or the WLS effectintroduces a delay that modifies the pulse distribution. IOR gradientstructures (similar to the concept of SELFOC microlenses) can be createdby ion implantation.

Scintillator rod geometries can benefit from the introduction ofinternal structures (FIGS. 2 c-2 g) such as segmentation 205, boreholes208, 1-D sub-rods 215, and 2-D sub-rods 216. Segment surfaces can bemodified using one or more surface treatment techniques (manipulatingreflection 206, absorption, IOR mismatches, IOR gradients, roughness,shallow surface cuts, WLS materials, applying coupling structures suchas very thin focused fiber bundle layers or SELFOC micro-lenses tocreate patterns that will control how the light is transmitted,reflected, or absorbed at the segment interface. For example, a thinarray of focused fiber bundle or a SELFOC microlens array could be usedto enhance propagation in one direction between two adjacent segments. Apattern of angled cuts or surface etching or ion implantation could alsobe used to create a shallow focusing pattern 207 similar to a microlensarray (FIG 2 e). Additional directionality can be achieved byintroducing a reflective material in between the apertures of thefocused pattern. The segment surface modifications can be variedaccording to location with respect to the readout interface(s) in orderto control how a light signal will be distributed to the readoutphotodetector(s). Boreholes can be continuous or partial. Partialboreholes do not extend all the way through the scintillator rod andthus serve a role intermediate between surface treatments such asshallow surface cuts and continuous boreholes with respect to modifyinglight propagation. In addition a continuous or partial borehole can bephysical (created by ablation, cutting, milling, or drilling) or virtual(created by modifying the scintillator material IOR or absorptionproperties locally using techniques such as ion implantation, laserheating, or controlled doping). A particularly simple way to introduceboreholes with simple or complex shapes into a rod is to form theboreholes at the interface surface between rod segments. Completeboreholes are formed by bringing the two segment surfaces together. Thesize, shape, internal coatings, and distribution of physical boreholescan be manipulated in order to control (encode) how light propagatesthrough and around a rod. For example, surface treatments such asreflecting or WLS films can be applied to specific areas on the boreholewalls. Internal structures comprised of passive materials (such asfibers, spheres, etc.) and active materials (including scintillators,photoconductive and photoemissive photodetectors, and convertingmaterials such as single or multiple WLSs, WLS fibers, gases, etc.) canbe introduced into a borehole, providing additional means of encoding(and in some cases recording) the signal. (Note that internal structuressuch as boreholes can be aligned across rods and connected to a readoutthat provides SAR information in a manner similar to block geometries(FIG 9).) The surface treatments and internal structures such assegments and boreholes can also be applied to sub-rods.

Rod (and sub-rod) geometries with a segmented internal structures canfurther encode the segments using different materials in order toutilize pulse property (pulse shape, color) techniques (FIG 2 c).

Structured Light Sharing Rod Geometries.

Specific surface treatments applied to a rod can create 1-D (2-D)continuous or discrete shared windows. A 1-D shared window pattern 303of absorptive or reflective stripes can connect two adjacent rods withinor between layers (FIG 3 a). This window pattern can be limited tocoupling two adjacent rods (a 2-rod cell), three adjacent rods, etc. orused to couple all of the adjacent rods within a row or column of rods.A 2-D shared window pattern 304 can connect two adjacent rods within andbetween layers (FIG 3 b). This shared window implementation can belimited to coupling four specific adjacent rods (a 4-rod cell). Largercells can be formed up to the limit in which all adjacent rodsthroughout the 2-D array of rods are coupled. The two 1-D windowpatterns that comprise the 2-D shared window can be asymmetric. A simpleasymmetry results if the two 1-D window patterns are shifted or offsetwith respect to each other (FIG 3 b). This creates an asymmetry thatrepresents an additional means of encoding the signal. Another means ofintroducing an asymmetry is by using two distinctly different 1-D windowpatterns. (This approach can be used with the 1-D shared window of FIG 3a for the continuous case by employing asymmetric 1-D window patterns onopposites sides of a scintillator rod.) Surface treatments techniques(including the use of WLS materials and coupling structures such as verythin fiber (or focused fiber) bundle layers or SELFOC microlenses) canbe employed to create the desired window pattern. (Note that thethickness or the width of the scintillator rods could be increased ifthe readout signals between adjacent rods demonstrate a measurabledependence on the event location with respect to the interface betweenrods.) The concept of shared window patterns can be used with both rodsand sub-rods. A novel implementation of this shared window design (FIG 4a) is to define a window by cross-coupling alternate layers ofscintillator rods 202. This cross-coupled window can be used to connectall layers or a specific subset of layers such as two adjacent layers.This cross-coupled window can be further defined by imposing anadditional shared window pattern between cross-coupled scintillatorrods. Yet a further extension of this concept is to cross-couple layerscomprised of two-rod cells (or four-rod cells). For the cross-coupledrod case 2-4 1-D, 2-D, or PSAPD photodetector readout arrays can beemployed. Since there are gaps between consecutive, aligned scintillatorrod layers, detector design requirements can be modified to use thedetector area that corresponds to the gaps to improve detectorcapabilities. Improvements might include reduced leakage betweendetector elements, increased charge storage capacity, additional on-chipelectronics, an increased amplification volume, and faster responsetimes. A related design cross-couples a planar array of scintillatorrods 202 to an array of conventional or WLS fibers 404 orphotoconductive strips to provide SAR information (FIG 4 b). Fibers canbe readout using one or more photodetector designs including, but notlimited to, (strip) SSDs, SiPM arrays, internal discrete amplificationphotodetector arrays, 2-D APD arrays, PSAPDs, or SA-PSAPDs (strip arrayPSAPDs). If the rod array is segmented using different materials, colorfilters can be applied to the fibers in a pattern that matches thepositions of the materials. This will help reduce the level of opticalsignal entering a particular fiber from adjacent scintillator segments.The fibers used with an edge-on SAR scintillator rod array can be muchshorter than fibers used to readout existing face-on block scintillatordetector designs.

The offset segment design involves shifting alternate rows of lineararrays of discrete scintillator rod segments by (typically) one-half rodsegment causing the signal to split in a branching pattern. A 1-D offsetrod segment design 502 is shown in FIG 5 a. By extension signalsplitting can also be enabled between layers in a continuous manner or acell configuration of two (or more) layers 503 (FIG 5 b). Surfacetreatment techniques, internal structure techniques, and structuredlight sharing techniques (such as shared windows) can be applied tofurther encode the light signals by controlling light propagation andpulse properties.

The structured light sharing geometry can also exploit pulse propertiessuch as pulse shape and color to determine the interaction positionwithin a cross-coupled scintillator rod array, a fiber array, or offsetpixel segments.

The edge-on SAR scintillator single rod and structured light sharing rodgeometries can be used within the same edge-on SAR scintillator detectormodule.

Structured light sharing and single scintillator rod geometries can beimplemented with a one-side or a multi-side (typically two-side)readout. Single scintillator rod geometries typically utilize a two-sidereadout since the one-side readout format requires an assumption thatdetected signals are due to photoelectric interactions. In manyinstances the one-side readout implementations of the edge-on SAR roddesigns emulate the face-on DOI rod designs described in the literature.An advantage of the edge-on SAR scintillator rod approach is that theimplementations of detector properties such as the dimensions ofscintillator rods, rod segments, surface treatments, internalstructures, and pulse properties are no longer constrained by the needfor a scintillator rod to provide a reasonable level of detectionefficiency (such as scintillator rods with lengths of 30 mm for PETimaging). An edge-on, SAR scintillator rod design can implement arelated face-on, DOI scintillator rod design “as is” (if it alreadyprovides adequate spatial and energy resolution) or in an aggressivemanner.

There are two categories of scintillator block geometries that may besuitable for implementation as edge-on SAR scintillator detectormodules: the narrow, 2-D SAR scintillator block (sheet) and the broad,3-D SAR scintillator block. The sheet thickness typically defines one ofthe spatial resolution dimensions. Once again the choice ofconfiguration and optimization technique(s) for a SPECT or PET edge-onSAR scintillator detector module will be the result of numeroustrade-offs: the desired spatial resolution and uniformity, energyresolution, pulse properties (pulse shape, spectrum), scintillator IOR,energy-dependent conversion efficiency, stopping power, the energyrange, the photodetector readout, the count rate, and the imaginggeometry (planar or ring, large or small volume).

The broad, edge-on, 3-D SAR scintillator block detector with either aone-side readout 600 (emulating a broad, face-on, 3-D DOI scintillatorblock detectors) or a multiple-side readout can be implemented (FIG 6).A multiple-side readout offers improved spatial resolution but it ismore expensive to implement. Multiple edge-on, 3-D SAR scintillatorblocks 615 (possibly using different dimensions and/or differentmaterials) can be stacked.

Edge-on SAR scintillator sheet designs include vertical or horizontalstacks of edge-on SAR scintillator sheets 715 (FIG 7). Sheet thicknessand material can be varied as needed. Edge-on SAR scintillator sheet canbenefit from the surface treatments, internal modification, andstructured light sharing techniques developed for edge-on SARscintillator rod detector geometries. These techniques include uniformand patterned surface treatments (modifying absorption, reflection, IORmismatches, IOR gradients, spectral properties (using WLS materials),and scattering properties as a function of position by applyingcoatings, controlling surface roughness, and introducing shallow surfacecuts) or the use of internal structures such as sub-sheets (similar tothe concept of sub-rods) and borehole arrays 805 (FIG 8). Controlleddoping of an activator material in a 2-D pattern could be used tospatially encode pulse properties. The same surface treatments, internalstructures, and structured light sharing techniques used with sheets canbe applied to sub-sheets. (Note that uniform and non-uniform boreholearray designs can be implemented. For example, borehole patterns thatsimulate single rod designs such as segments (uniform grid patterns) andoffset segments (offset grid patterns) can be employed.) Internalstructures such as boreholes 805, as described for edge-on SARscintillator rod arrays, can be aligned across edge-on SAR scintillatorsheets and connected to a readout by fiber optics 900 or other meansthat provides the SAR information (FIG 9). In addition, edge-on SARscintillator sheets can be placed between crossed (conventional or WLS)fiber arrays. Readout can be from 2, 3, or 4 sides. (For example, onereadout configuration consists of a strip photodetector coupled to theedge that is used to estimate the optical energy within a sheet while1-D arrays of photodetector determines the x and y axis position basedon reading crossed fiber arrays coupled to the upper and lower faces ofthe scintillator sheet. If only a single fiber array is employed todetermine x and y position then it requires a dual readout.) A novelvariant of the 1-D continuous or discrete shared window design betweenadjacent rods can be extended into a 2-D continuous or discrete sharedwindow design between adjacent sheets. This design can be used toimprove spatial resolution. Optionally, a reduction in the number ofreadout surfaces may be practical. (Note that the thickness of thesheets could be increased if the readout signals between adjacent sheetsdemonstrate a measurable dependence on the DOI position (sub-DOIresolution).)

The advantage of the edge-on SAR scintillator block design with respectto face-on scintillator block designs is that detector properties suchas the dimensions of scintillator blocks, surface treatments, or thecreation of internal structures are not constrained by the need toachieve a reasonable level of detection efficiency or a large detectorsurface area. Both of the edge-on SAR scintillator block geometries canexploit the layered “multiple scintillator material” capabilitydiscussed for edge-on SAR, scintillator rod geometries. In addition,both edge-on SAR scintillator block geometries can be used within thesame edge-on SAR scintillator detector module. If advantageous, edge-onSAR scintillator block and rod geometries can be used within the sameedge-on scintillator detector module. (For example, if resolutionrequirements are depth-dependent.) Furthermore edge-on SAR detectorgeometries can be combined with basic edge-on and/or face-on detectorgeometries to create hybrid edge-on SAR detector modules. For example, ahybrid edge-on SAR detector module suitable for use in a Compton gammacamera would use a face-on, planar 2-D Si or Ge array as the Comptonscatterer followed by an edge-on SAR scintillator detector. In adifferent application the face-on, planar 2-D Si or Ge array might beused to detect particles such as electron while the edge-on SARscintillator detector might be used to detect photons or otherparticles.

The enhanced capabilities of specific edge-on SAR scintillator rod andblock detectors detailed herein can be appreciated within the context ofexisting DOI scintillator detector designs. Face-on, scintillator DOItechniques developed for high resolution PET include readout from frontand back ends of a scintillator array (dual or two-side readout withphotodetector arrays), “Phoswich” (a phoswich, or “phosphor sandwich”,is a combination of scintillators with different decay time constants),offset front and back scintillator arrays, light sharing betweenadjacent scintillator elements, pulse shape discrimination, etc. Theedge-on SAR scintillator detector modules that are motivated by theface-on DOI techniques can be used to construct high-resolution SPECT,PET, and Compton gamma cameras (as well as SPECT-PET cameras, hand-heldSPECT or PET cameras, and non-medical imaging systems). Calibration ofthe edge-on scintillator detector modules is required in order todetermine the signal strength versus photon interaction location withinthe scintillator element. Face-on DOI calibration techniques can beemployed for this purpose, Huber J., et al., IEEE Trans. Nucl. Sci. Vol.45, No. 3, pp. 1268-1272, June 1998 and Vaquero J., et al., IEEE Trans.Med. Imag. Vol. 17, No. 6, pp. 967-978, December 1998.

In both face-on DOI and edge-on SAR scintillator detector designs aone-side or a multi-side readout can be implemented. The multi-sidereadout designs typically provide improved DOI or SAR information but ata greater cost. (If the cost of a readout detector is significant thenthe relative advantage of a dual-readout design versus using twoone-side readout designs is no longer guaranteed.) The two-side (dual)readout designs are frequently used with face-on scintillator rod arraydetectors because of the improved DOI response uniformity and thereduced ambiguity in the measured signal strength. Edge-on SARscintillator detector likewise benefit from a two-side readout design. Avariety of photodetectors such as photomultiplier (PMT), flat PMTs, PMTarrays, position-sensitive PMTs (PSPMTs), APDs, PSAPDs, silicon driftdetectors (SDDs), SiPMs, internal discrete amplification photodetectors,photodiode arrays, HgI₂ arrays, etc. have been used with face-onscintillator detectors. The problem with using the dual readout DOItechnique in face-on, high resolution PET (511 keV photons) imaging isthat the scintillator rods have to be narrow for high resolution butthey have to be long to efficiently stop 511 keV photons. Thesubstantial length (on the order of 30 mm for a clinical system)degrades the DOI resolution and the energy resolution (due to opticalsignal losses). An unavoidable problem with face-on, dual-readoutdesigns is that the front photodetector array is directly exposed togamma rays.

An additional problem is that Compton scattering of incident radiationis biased in the forward direction such that the probability ofdetecting the scatter event downstream from the initial event in thesame scintillator rod is not small (resulting in an inaccurate DOIestimate). The edge-on SAR scintillator rod detector design reduces thelikelihood that a Compton scatter photon will be detected in the samescintillator rod. Tracking algorithm techniques developed for particledetectors and medical imaging should be highly effective due to thereduced overlap of primary and secondary events. The edge-onscintillator detector module format may reduce the cost of using certainscintillator materials. Blocks and rods with smaller dimensions (forexample, a scintillator rod length of 10-20 mm versus 30 mm) may havehigher manufacturing yields if the scintillator is difficult to grow inbulk or to machine.

This invention emphasizes novel and improved designs that encode howlight pulses are distributed within and/or between edge-on SARscintillator detector elements (rods or blocks) and thus the lightsignal distribution that reaches one or more readout surfaces.

Techniques for encoding edge-on scintillator elements may includemodifying the side walls, creating internal structures within anelement, sharing the light pulse between elements, and the use ofmultiple scintillator materials (pulse properties). Advantages of theedge-on SAR scintillator detector approach include the use of moreaggressive implementations of existing DOI techniques and the ability toimplement entirely new encoding techniques. The use of a particulartechnique or a particular implementation of a technique depends on thescintillator material properties as well as the dimensions of thescintillator element (rod or block).

Surface treatment techniques are frequently employed in order to modify(encode) the scintillator signal distribution at a readout surface.Surface treatment techniques used to alter one or more of thescintillator element surfaces (in some cases, the readout surface) as afunction of position include ion implantation (altering the IOR),etching (varying the degree of surface roughness), cutting shallowsurface patterns (straight or angled, crosscut, variable angle or depthwith position, alternating patterns, etc.), and applying absorptive orreflective coatings in patterns, etc. A fraction of the scintillationsignal is attenuated or redirected. Researchers have evaluated a numberof surface treatment schemes including varying the degree of roughness,the use of specular (mirror and directional) and diffuse reflectivecoatings, absorptive paint patterns, surface cuts, etc. in order tocontrol the scintillator rod light distribution for DOI information, seee.g., Burr K., et al., IEEE Trans. Nucl. Sci. Vol. 51, No. 4, pp.1791-1798, August 2004, and Rothfuss H., et al., IEEE Trans. Nucl. Sci.Vol. 51, No. 3, pp. 770-774, June 2004, and Shao Y., et al., IEEE Trans.Nucl. Sci. Vol. 49, No. 3, pp. 649-654, June 2002.

Internal structures can be introduced into a scintillator rod or sheet.Segments (surfaces with IOR mismatches; reflective, absorbing, orfocusing patterns), sub-rods, and borehole patterns (physical holes orinduced IOR modifications of various shapes) can be added toscintillator rods. The material can be varied by segment (if desired) inorder to exploit pulse properties using pulse shape analysis (PSA) orcolor information. Continuous and partial borehole patterns implementedwith physical and virtual boreholes can be added to scintillator sheets.Physical borehole can be left as open holes, coated (with directional ornon-directional coatings that may be reflective, absorptive, WLS,photoemissive, photoconductive, etc.), or filled with a material such asphotodetector or fiber (conventional or WLS). Borehole patterns can beused to help channel the spread of a light signal within thescintillator material.

Sharing the light pulse between scintillator rods can include couplingby shared windows or offset segments. Shared windows can result fromcontinuous contact or discrete windows (created by surface treatments,cross-coupled alternate layers of scintillator rod arrays via continuouscontact or discrete windows, or thin fiber bundle layers). An example ofoffset segments is a row of scintillator elements in a 2-D array that isoffset or shifted with respect to the adjacent rows. The offset elementgeometry may reduce imaging problems related to spatial resolutionartifacts. Materials can be varied in order to utilize PSA and/or colorinformation. Thus the scintillator rods coupled by continuous contact ordiscrete windows could be segmented scintillator rods that use more thanone scintillator material. Individual scintillator arrays of rods in across-coupled geometry could each use a distinct material and byextension, provide additional encoding of rods within an array. Theelements in the offset element geometry can use more than one material.The use of multiple scintillator materials exploits the well-knownconcept of encoding position within a detector plane based on pulseshape. (A novel feature is to encode position within a detector planebased on spectral distribution. This requires color-sensing capabilityusing either color filters with the photodetector readout detector or byexploiting the response characteristics of the photodetector readoutdetector.)

Thus encoding techniques developed for one-side or two-side (ormulti-side), face-on DOI scintillator elements (rods and blocks) can beapplied aggressively to edge-on SAR scintillator elements. In addition,novel encoding techniques can be applied to edge-on SAR scintillatorelements.

The flexibility of the edge-on SAR scintillator detector approach isdemonstrated by the ability to manipulate parameters such as thescintillator material or cross section as a function of depth and thusmanipulate the response to incident radiation parameters such as theradiation type, energy, polarization, spin, etc. (The basic edge-onscintillator array with DOI capability is described in Nelson, U.S. Pat.No. 4,560,882.) In addition, a number of readout detector configurationsare permitted.

It is straightforward to layer (stack) different scintillator materialswithin an edge-on SAR scintillator detector module in order to imageradiation with multiple energies (such as a SPECT-PET gamma raydetector) or multiple radiation types (such as photons and neutrons,electrons, etc.). In addition face-on scintillator and non-scintillatormaterials (attenuators, converters, polarizers, and sensors such assemiconductor arrays, microchannel plate, amplifiers, gases, etc.) canbe positioned adjacent to edge-on SAR scintillator layers in order todetect or attenuate radiation particles with different energies orproperties (including primary or secondary radiation), or to act asradiation converters. (Radiation converters have been used in highenergy physics, gamma ray astronomy, neutron imaging, and high energyindustrial radiography and radiation therapy imaging.) Thus,multi-material edge-on SAR scintillator detector modules can beconstructed from more than one scintillator material and fromcombinations of scintillator and non-scintillator materials.

Detector module designs utilizing material depth-dependence would besuitable for multiple-energy SPECT imaging or SPECT and PET imaging.(The design could also be used to image multiple types of particles,such as beta emissions and gamma rays or x-rays, at the same time.) ASPECT-PET camera might use a scintillator material such as NaI(Tl),LaBr₃ or CsI(Tl) for imaging low energy gamma rays followed by LSO forimaging 511 keV gamma rays. LSO could represent a problem for SPECTimaging. The radiation from ¹⁷⁶Lu could introduce a background signal inthe low energy detector material. This background signal in the lowenergy detector material can be reduced by using energy windows toreject a fraction of the background events. Further reductions arepossible by inserting a layer of an absorber material between the LSOand the adjacent scintillator materials.

An alternative is to modify the design and replace the radioactive LSOwith a different PET scintillator material. The layered scintillatormaterial design can be employed even if only one photon (or particle)energy is imaged. If scintillator elements in adjacent layers of rods(including crossed rods) or sheets employ structured light sharingtechniques (including shared windows with WLS materials) then thematerials in adjacent layers may be selected to have different pulseproperties (pulse shape, spectrum). Thus materials in adjacent layerscan differ according to composition (LSO, YLSO, GSO) or concentration ofan activator such as Ce in LSO. The edge-on SAR detector design ishighly flexible. Layering materials is not the only option. Scintillatorrod materials (and non-scintillator materials) can be varied within alayer to optimize the response to spatially-dependent radiation. Forexample the central region might detect photons or particles withspecific properties that differ from the outer regions or the centralregion might act as a converter or particle polarizer.

Although a uniform (“x”=“y”) rectangular cross section for thescintillator rods is straightforward to implement, non-uniformrectangular cross sections can be used. For example, the vertical (orDOI) resolution requirements may differ from the horizontal resolutionrequirements or they may vary with depth. A rod cross section in whichthe “x” and “y” values differ could allow a reduction in the totalnumber of scintillator rods required. Another example is the PET ringdetector design. A particular SAR implementation with rods in an axialorientation could form a set of concentric scintillator rings in whichrods have an annular cross-section as seen from along the axis of thering detector. In this case the edge-on SAR scintillator rod determinesthe axial resolution.

The choice of readout detectors (and costs) may be tailored to providediscreet or shared readout capabilities. The number of readout elementsneeded for high resolution SPECT, PET, and Compton imaging systems is aconcern for both face-on and edge-on detector designs. One method toreduce the number of readout elements is to share readouts across pixels(assuming acceptable detector dead time) was exploited in the originalAnger gamma camera. A single scintillation crystal was viewed by a 2-Darray of PMTs and the centroid of the signal is estimated. More recentdevelopments exploiting this approach incorporated into this inventioninclude position sensitive PMTs (PSPMTs) and PSAPDs (with readoutelectrodes at the four corners of a rectangle. These technologies can beutilized with the edge-on scintillator array design.

In another aspect, a readout technique originally developed forsemiconductor detectors, the cross strip array with perpendicular anodeand cathode strip arrays on opposite sides of the detector plane, can beused in this invention for scintillator arrays in either an edge-ongeometry (FIG 1) or a face-on geometry. A 1-D (linear) array of stripphotosensors (such as a PD or APD strip array) 100 is positioned on oneend of the scintillator rod array 102 and a second linear array of stripphotosensors 100 is positioned on the opposite end of the scintillatorrod array at right angles to the first linear array of stripphotosensors. Thus 3-D positioning for incident radiation 105 can bedetermined with 2 linear arrays of strip photosensors in edge-on orface-on geometries. Alternatives are a combination of two 2-D readoutarrays or a 2-D array and a 1-D array (which can be oriented to dealwith directional scatter). The combination of two 2-D readout arraysoffers the lowest readout noise (the readout surface area is matched tothe cross section of the scintillator rod) and the smallest dead time (apair of readout elements see a single scintillator rod, a pair ofcrossed strip readout elements see two crossed scintillator planes).Although the dual readout technique can be implemented with pairs of 1-Dor 2-D photodetector arrays or combinations thereof, it may beadvantageous to use even fewer readout elements. PSAPDs with only fourreadout electrodes (contacts) dramatically lower the readout elementcount, Shah K., et al., IEEE Trans. Nucl. Sci. Vol. 49, No. 4, pp.1687-1691, August 2002 (see FIG 1, p. 1688). Unfortunately the minimumdetector dead time will increase since multiple scintillator rods areviewed simultaneously by a single photosensitive surface.

A novel alternative to existing low-noise readout designs such as the(strip) SDD and the (area) PSAPD described by Shah are segmented SDD andPSAPDs. For example, the PSAPD is segmented into strips and thus forminga strip array PSAPD or SA-PSAPD (FIG 10 a). The SA-PSAPD divides thePSAPD active area into strips 1000 and uses two readout electrodes 1003located at the ends of the PSAPD strips rather than four readoutelectrodes located at the corners of a rectangle. The position of anevent along the length of the strip can then be determined by the chargesharing between two electrodes rather than four electrodes. The typicalreadout signal level per electrode should increase and the readout noiseshould decrease due to a reduction in surface area (capacitance) and thecomparison of two rather than four readout signals. Both PSAPDs andSA-PSAPDs provide 2-D spatial information. The SA-PSAPD providesdecreased detector dead time (since each strip looks at a single layerof the entire scintillator volume). SA-PSAPDs can be used for their 2-Dreadout capabilities in place of PSAPDs and 2-D APD arrays or simply asstrip arrays.

In one aspect, the invention provides multi-pixels SiPM designs andmulti-pixel internal discrete amplification photodetector designs inwhich a subgroup of pixels share a common output for the total energy ofthe signal and provide a weighted spatial location; in some aspectsthese are implemented to simplify readout requirements. In one aspect,if the photodetector pixels are sufficiently small that two or more arecoupled to face of a scintillator straw, then they can share a commonoutput for the total energy of the signal and provide a weighted spatiallocation. In one aspect, this weighted spatial location information isused to enhance the SAR or DOI position estimate since the opticalsignal distribution on the output face (or output faces) of ascintillator straw may be correlated to the event location within thescintillator straw. An alternative implementation is to retain the datafrom the individual pixels of the subgroup and apply sophisticatedpositioning algorithms similar to those used with conventional gammacameras that are readout by multiple PMTs or with block detectors.

The SA-PSAPD can be used to readout face-on DOI scintillator rod arraysand basic edge-on scintillator arrays (providing DOI information) aswell as edge-on SAR scintillator rod arrays. If used with a basicedge-on scintillator array DOI information may be controlled bysegmenting the scintillator rods (using IOR mismatches or reflectors)and using surface treatment techniques, Nelson U.S. Pat. No. 4,560,882.A problem may arise if individual SA-PSAPD strips are required to beexceedingly long in order to readout a long row or column ofscintillator rods, leading to excessive readout noise and/or deaddetector volume during an event. The SA-PSAPD strips can be segmentedinto sub-strips 1001 wherein each sub-strip has dual readout electrodes1004 located at the ends of the sub-strips (FIG 10 b). The number ofreadout electrodes in the SSA-PSAPD would increase relative to the dualreadout implementation but it could still be comparatively smallcompared to a full 2-D pixellated readout. The sub-strips within a stripcan have different lengths if needed to match a non-uniform scintillatorrod pattern. (Note that a similar modification to the detector elementgeometry of a 2-D photodiode (PD) or APD uniform pixel array wouldcreate a 2-D PD or APD sub-strip (pixel) array.) A strip SDD array canalso be divided into sub-strips (pixels). In this case sub-strip SDD(SS-SDD) arrays also benefit from a reduction in noise per readoutsub-strip and a reduction in detector dead time since each sub-stripviews far fewer rods simultaneously compared to a full strip. Theapproach of creating sub-elements of a standard detector element such asa strip can be applied to the PSAPD. For example, the area of a PSAPDcan be segmented into two, three, or more sub-areas (each with fourreadout electrodes), creating a sub-area array of PSAPDs (SAA-PSAPD).This design reduces readout noise and dead time compared to a large areaPSAPD and it views a different set of scintillator rods than what aSA-PSAPD views (a row or column). Note that both strip and sub-areaarray PSAPDs can be combined on the same readout detector (a mixed PSAPDdetector) permitting variable resolution to match specific scintillatorrod configurations. For example, depth resolution requirements (andsometimes 2-D spatial resolution requirements) may vary based on theradiation type and energy (multiple energy imaging with photon and/orparticle is encountered in nuclear medicine, radiation therapy, highenergy physics, astronomy, etc.). These additional readout detectoroptions permit a finer level of control as to readout noise, dead time,the detection of directional scatter, and cost. In some aspects, thesereadout geometries are implemented using SiPM arrays or internaldiscrete amplification photodetector arrays.

In another aspect, as an alternative to the strip photodetector readout,the invention uses a fiber strip array coupled to a low noise readout.The fiber can be conventional or a WLS fiber. In some aspects, the fiberreadout may be in terms of cost, limited interaction with incidentradiation or radiation by-products, or long-term reliability. Thesefiber strip arrays become more cost-effective to use relative tophotodetector arrays as the length of the fiber coupled to thescintillator material increases.

Although FIG 4 b shows the fibers coupled perpendicular to the length ofthe scintillator straws, in alternative aspects the fibers can also becoupled parallel to the length of the scintillator straws. Couplingbetween fiber and scintillator can be enhanced by implementing shallowangled cuts (or IOR changes) in the fiber to direct more optical photonstoward the readout end of the fiber. (This eliminates issues related tothe non-uniform detector volume created by making shallow cuts withinthe walls of the scintillator crystals.) Fiber readouts can be used withface-on, edge-on SAR, and crossed edge-on SAR detector configurations.Fiber readouts may be used to provide improved SAR, DOI, or timingresolution (in which the fiber signal is readout by a separate highspeed photodetector such as a SiPM or internal discrete amplificationphotodetector). Fiber readouts in general and fiber readouts withshallow angle cuts (or other surface treatments) in particular may beused to improve overall light collection efficiency and uniformity forface-on x-ray and nuclear medicine imaging applications (including handheld probes). In this instance the fibers are oriented parallel to thelength of the scintillator straws. Consider an area, slit, or slot (flator focused) face-on radiation therapy portal imaging detector (or aMega-voltage CT detector) with tall scintillator straws (mms to 10 s ofmms in length). Low energy x-rays preferentially stopped near the frontface produce smaller optical photon signals and lose a larger fractionof photons migrating toward the readout detector. Fibers with shallowangled cuts could be coupled parallel to these fiber straws edge-on andreadout with the same photodetectors that the scintillator straws use.

The improved techniques and novel readout detectors described herein tocreate high resolution edge-on SAR detector modules may be implementedwith face-on DOI rod and block detectors in order to improve DOIresolution.

Planar and certain ring detectors assembled from edge-on SARscintillator detector modules benefit from the use of relatively thin,low-noise photodetector arrays such as PD arrays, APD arrays, PSAPDs,SDDs, SiPMs, internal discrete amplification photodetectors, HgI₂ array,new segmented arrays, etc. Thin detectors minimize the dead spacebetween adjacent detector modules. Edge-on scintillator detector modulesthat use PMT arrays (or PSPMTs) for readout tend to limit the concept ofa detector module. The PMT arrays are too thick to build arrays ofdetector modules with non-intrusive gaps between detector modules. Thislimitation of PMT arrays is highlighted by recurring efforts toimplement an axial-on (edge-on SAR) scintillator ring detector for PETimaging.

The axial-on scintillator ring detector for PET is a non-modular singledetector ring comprised of edge-on scintillator rod elements alignedwith the axis of the PET system. Thick photoemissive detectors such asPMTs or position sensitive PMTs (PSPMTs) provide a dual readout. Thethickness of the PMT arrays at the ends of the rods is sufficientlylarge that prohibitively large gaps would exist between adjacentdetector rings. This detector design is highly constraining since thelength of the scintillator rods must be sufficiently great (at least 100mm) to image a small organ or small animal which in turn requiresreadout photodetectors (PMTs) that provide very large signalamplification and dynamic range (due to the significant light lossesthat may occur within the extremely long scintillator rods). Anotherdrawback of the axial-on scintillator ring detector design is the costof manufacturing very long scintillator rods. (Not all scintillatormaterials can be grown in a large boule format like NaI(Tl) and CsI(Tl)or processed as a ceramic.) An early example of this approach wasimplemented in the PETT-IV system in which a ring of NaI(Tl) rods (50 mmdiameter, 170 mm long) were coupled to PMTs at both ends, Mullani N., etal., IEEE Trans. Nucl. Sci. Vol. 25, No. 1, pp. 180-183, February 1978.The axial-on SAR was 16 mm FWHM. Shimizu described a PET ring detectorthat used arrays of 3×5×50 mm³ BGO crystals coupled at both ends to aposition sensitive PMT (PSPMT), Shimizu K., et al., IEEE Trans. Nucl.Sci. Vol. 35, No. 1, pp. 717-720, February 1988. The average axial-onSAR was 9.5 mm FWHM. The possibility of extending the length to 100 mmwas discussed. A recent study by Braem involved coupling a 2-D hybridphotoemissive-photodiode array to each end of a scintillator array using3.2×3.2×100 mm³ YAP crystals, Braem A., et al., Nuc. Instr. Meth. Phys.Res. A Vol. 525, pp. 268-274, 2004. Braem “estimated” that with improvedsystem components an axial-on SAR uncertainty on the order of 5 mm FWHMwas possible. This predicted “attainable” SAR is not considered to be“high-resolution” (typically 1-3 mm) by current PET standards.

This non-modular, axial-on scintillator ring detector design can be madesomewhat-modular and thus extended to a detector array of two rings (inone aspect, comprise shorter scintillator rods) if at one end of thescintillator rod array the PMT array is replaced by a thin PSAPD, SiPMarray, internal discrete amplification photodetector array, APD array,or SDD array (for example). In one aspect, butt the ring detectors atthe sides with the thin PSAPD, SiPM array, internal discreteamplification photodetector array, APD array, or SDD arrays. A modulardesign is possible if only thin PSAPDs, SiPM array, internal discreteamplification photodetector array, APD arrays, or SDD arrays are used toreadout the ends of the rods. Then a modular, axial-on ring detectorcomprised of multiple axial-on detector modules can be assembled. Theaxial-on design employed by Braem is implemented using the conventional,two-side readout format. The edge-on SAR detector module design foraxial-on imaging can be implemented using either the one-side ortwo-side readout format. The flexibility of the edge-on SAR scintillatordetector format permits an alternate modular, axial edge-on SARscintillator ring detector for PET that eliminates the need to buttaxial-on scintillator detector modules (FIG 11 a). (Note that if thegaps between adjacent edge-on SAR scintillator detector modules 1100shown in FIG 11 a are sufficiently large then the requirement for thinphotodetectors can be relaxed. Relatively thin photoemissive detectorscould be employed. Another example is hand-held detectors (includingsurgical probes) that use a single edge-on SAR scintillator detectormodule with a two-side readout or butted edge-on SAR scintillatordetector modules with one-side readouts could also use relatively thinphotoemissive detectors coupled to the exterior scintillator surfaces.)

Although a uniform rectangular geometry using scintillator rods with auniform rectangular cross section is straightforward to implement foreither design (FIG 11 a) a limitation is that radial gaps will bepresent in the ring detector volume. This effect can be mitigated forthe axial-on SAR scintillator ring geometry by using scintillator rodswith a “non-uniform” wedge-shaped cross section (an annularcross-section 1102) that expands as the radius increases (FIG 11 b).Changes to the scintillator rod design parameters may be needed in orderto compensate for the effect of the non-uniform cross section on thesignal distribution. Planar readout devices can still be employedalthough a PSAPD readout simplifies the need for a custom readout devicewith non-uniform pixel elements. The modular, axial edge-on SARscintillator ring detector permits a different solution to the problemof gaps in the scintillator volume. The ends of an array of rectangularedge-on scintillator rods can be cut at an angle creating atruncated-triangle (wedge) geometry 1103 as seen from a side perspective(FIG 11 c). This eliminates the cost of manufacturing detector rods witha non-uniform cross section and permits the use of uniform planarreadout devices such as strip array and 2-D photodetectors (as well asPSAPDs). The scintillator rod design parameters need to be modified tocorrect for the fact that the rod length increases with radius in thisdesign. For both axial-on and axial edge-on SAR scintillator detectordesigns can be implemented with scintillator blocks in place ofscintillator rods.

Although the embodiments of the present invention have been described interms of its use for nuclear medicine (SPECT, PET, Compton camera,SPECT-PET camera, and hand-held SPECT or PET camera) imagingapplications, the present invention may also be used for other medicalradiographic imaging applications such as radiation therapy portal andCT imaging, PET-CT imaging, as well as industrial and scientificapplications. Edge-on scintillator detector modules with SAR capabilitycan be used not only for medical imaging applications but alsonon-medical applications such as mine detection, military and hazardousradiation material detection, neutron radiography and CT imaging, highenergy physics, and astronomy. Other suitable applications that employhigh energy photons include industrial radiography and CT imaging. Forconventional fan-beam CT imaging (rather than cone-beam CT imaging) itis convenient to have the apertures (unless they extend for only a fewpixels) positioned parallel to the CT axis (axial-on). If x-ray fluencerates are too high to exploit SAR effectively then basic edge-onscintillator designs (Nelson, U.S. Pat. No. 4,560,882) should beemployed. Then, at least in this aspect, it is preferred to position thedetector planes parallel to the CT axis (Nelson, U.S. Pat. No.6,583,420). Thus the modular, edge-on scintillator ring detector designis suitable for high resolution PET, CT, and by extension PET-CT systemsusing either edge-on SAR scintillator modules or basic edge-onscintillator modules.

Edge-on Imaging Probe Detectors

The invention also provides edge-on imaging probe detectors for use innuclear medicine, such as radiation therapy portal imaging, or for usein nuclear remediation, mine detection, container inspection, and highenergy physics and astronomy. The invention provides products ofmanufacture, apparatus, devices and designs for edge-on imaging probedetectors for a variety of purposes, including medicine, e.g., nuclearmedicine, homeland security, including airport, train, border, or port(ship) security (e.g., inspecting shipping containers, cargo, bags,cars, trucks and the like), and the like.

In alternative aspects, edge-on detector modules of the invention cancomprise edge-on scintillator and/or semiconductor detectors, readoutand processing electronics, power management, communications,temperature control, and/or radiation shielding, as well as severaledge-on detector module array configurations, e.g., as described inNelson, U.S. Pat. No. 6,583,420; Nelson, U.S. Pat. Appl. publication No.20040251419; Nelson, U.S. Patent Office Disclosure Document No. 567471.Elements of SAR edge-on semiconductor and scintillator detector modulesand gamma cameras that can be incorporated into the products ofmanufacture, apparatus, devices and designs are described, e.g., inNelson, U.S. Pat. Appl. publication No. 20040251419; Nelson, U.S. Pat.Appl. No. 60/667,824. Specific 1-D and 2-D edge-on scintillator andsemiconductor detectors (including DOI capability) without SARcapabilities are described in Nelson, U.S. Pat. No. 4,560,882 andNelson, U.S. Pat. No. 4,937,453. Exemplary manufacturing techniques tobuild structured 1-D and 2-D scintillator arrays of the invention forradiation detection are described, e.g., in Nelson, U.S. Pat. No.5,258,145.

An exemplary detector configuration for edge-on semiconductor andscintillator imaging probe detectors will be the result of numeroustrade-offs: detector surface area, desired spatial resolution anduniformity, energy resolution, pulse properties (pulse shape, spectrum),signal readout electronic circuitry, scintillator IOR, energy-dependentconversion efficiency, stopping power, the operational energy range, thetypes of particles, the scintillator photodetector readout, and themaximum count rate. For example, the choice of scintillatorphotodetectors (and costs) may be tailored to provide discreet or sharedreadout capabilities. In addition to silicon drift detectors (SDDs),photodiode arrays, Geiger-mode silicon photomultiplier (SiPM) arrays,internal discrete amplification photodetector arrays, and APD arrays,position-sensitive APDs (PSAPDs) may be used to reduce the number ofreadout elements (Shah K., et al., IEEE Trans. Nucl. Sci. Vol. 49, No.4, pp. 1687-1691, August 2002). Unfortunately the minimum detector deadtime will increase. An intermediate approach is the use of segmented SDDand PSAPDs (Nelson, U.S. Pat. Appl. No. 60/667,824). A number ofsemiconductor detector architectures are suitable for use in edge-onimaging including (but not limited to) single elements, strip arrays,crossed strip arrays, pixellated arrays, and ‘3D’ designs in which the‘p’ and ‘n’ readout electrodes are perpendicular to the surface (MorseJ, et al., Nuc. Instr. Meth. Phys. Res. A 524, pp. 236-234, 2004).

In one embodiment of the invention, as illustrated in FIG 12 a, adetector array 1000, can incorporates separate, discrete detectormodules 102, illustrated here as 1-D, edge-on strip detectors 101,configured in a planar geometry to optimize the detection of incidentradiation 107. Detector modules 102 utilize 1-D or 2-D array detectorsthat can have different properties. Each module 102 also includes a base106 and a communications link 103. The base 106 can comprise detectorelectronics, power management components, temperature controlcomponents, and a data or information channel for communicating with acomputer system. The base 106 may also incorporate a module electronicreadout unit that includes a signal conditioner or filter, an amplifier,an analog-to-digital converter, and a communication interface.Additionally, the detector module 102 may be coupled to anelectronically-controlled thermoelectric cooler or other temperatureregulating device that resides in the detector module base 106. In thisembodiment, the temperature-regulating device provides temperaturecontrol for the detector module 102 and its electronic readout unit. Thecommunications link 103 provides power to the module 102 and connectsthe base 106 to a computer system. Through the attachment with the base106, the link 103 enables a computer system to monitor and adjust themodule 102 electronic settings and temperature as well as setting anyapplication-dependent configuration parameters. The communication link103 can be used to off-load the digitized detector radiation data to acomputer system for analysis, image reconstruction, and data storage.

Basic Edge-on Imaging Probe Detector Geometries

Arrays of basic edge-on semiconductor and scintillator detector planesare available in 1-D (strip) and 2-D (crossed strip, pixellated, 3Ddesigns, etc.) geometries, and these can be used to construct 2-D and3-D imaging probes of the invention. Variations of these designs of theinvention include stacking (layering) basic edge-on arrays as well ascombining basic edge-on semiconductor and scintillator detector planeswithin a single imaging probe.

For example, in one aspect, a central detector comprising an array ofbasic edge-on scintillator or semiconductor planes could be surroundedat the periphery by basic edge-on scintillator or semiconductor planes(with a collimator in between inner and outer groups of detectors) tocreate an edge-on dual-detector probe (Hickernell T., et al., J. Nucl.Med. Vol. 29, No. 6, pp. 1101-1106, June 1988). In this aspect, thebasic edge-on detectors positioned at the periphery would be used tomeasure the background radiation signal while the central detector wouldbe used to locate the tumor.

FIG 12 a illustrates a perspective view of an exemplary array 1000 ofbasic, 1-D edge-on semiconductor detectors 101 assembled as a 2-Dedge-on detector array used in an edge-on imaging probe detector. FIG 12b illustrates a perspective view of an array of basic, 1-D edge-onsemiconductor detectors 101 assembled as a 4-quadrant edge-on detectorarray with an internal collimator 120 (not shown) used in an edge-onimaging probe. The use of 1-D edge-on semiconductor detector arrays withan aperture height of 3 mm and a strip length of 12 mm provides animaging probe detector with an active area on the order of 24×24 mm².The internal collimator consists of a pair of crossed tungsten or leadsheets creating 4 quadrants. Although the x-y spatial resolution islimited compared to the detector array shown in FIG 12 a there is nowDOI capability (z resolution) that can be used to distinguish differentparticles and their energy dependencies. This 4-quadrant edge-ondetector with an internal collimator can be used in place of an array ofbasic edge-on detectors to form the central detector of an edge-ondual-detector probe.

FIG 13 a illustrates a perspective view of an exemplary butted pair ofbasic, 1-D edge-on semiconductor detectors 101 with variable anode strippitch 126 near the radiation 107 entrance surface suitable for use in a4-quadrant edge-on imaging probe detector. For the scintillator case therod material has also been altered to reduce interactions with highenergy x-rays and gamma rays. The 2-D resolution shown in FIG 12 a canbe maintained while adding limited DOI resolution (and so reducing thenumber of readout elements relative to using basic, 2-D edge-on planarcrossed strip with a uniform strip pitch). FIG 13 b illustrates aperspective view of an array 1000 of limited, basic, 2-D edge-onsemiconductor detectors with segmented anode readout strips 130. In thisspecific case there is a variable anode strip pitch along the verticaldirection near the entrance surface. The choice of whether to use anodeor cathode readout strips may depend on the choice of semiconductormaterial and readout circuitry.

FIG 13 c illustrates a perspective view of an array 1000 of limited,basic, 2-D edge-on semiconductor detector 138 with anode readout stripsand crossed cathode readout strips 134 with a variable cathode strippitch near the entrance surface. This limited “crossed strip” design canbe used to emulate the DOI capability of the design in FIG 13 b. Thislimited segmented cathode designs provides limited DOI capability. Inone aspect, when DOI information is combined with energy resolutioncapability it permits rejection of high energy events that lose only afraction of their energy and thus appear to be acceptable low energyevents. The technique of implementing a variable readout element pitchin order to limit the total number of readout elements can be employedwith not only strip detector but also pixellated and 3D detectors.

In one aspect, pixellated and 3D detectors are used, and they offeradditional flexibility since a variable readout element pitch could beimplemented within specific rows and columns. For example, a fine rowand column pixel pitch could be implemented close to the detectorentrance surface while a coarse row and column pixel pitch could beimplemented further from the detector entrance surface. Another aspectof the invention implements a fine column pixel pitch near the detectorcenter and a coarse column pixel pitch near the detector periphery whilemaintaining a fixed row pixel pitch. A 2-D implementation of this designcan be assembled using an array of 1-D strip detectors as shown in FIG12 a but with a variable strip pitch between the detector center and theend along the horizontal direction.

In one aspect, manipulation of columns of detector elements, such aspixels or vertical strips, is done to introduce additional flexibility.In one aspect, specific detector elements such as vertical strips orcolumns of pixels can be ignored, either by not reading them or byreading them and not including their data during image reconstruction.The ignored detector elements such as strips or columns of pixels areessentially inactive for purposes of data processing. In one aspect,selective patterns of ignored vertical strips or columns of pixels arearranged to act as buffers between sets of active vertical strips orcolumns of pixels, providing internal collimation. In this case theedge-on probe detector implements an “electronic” internal collimatorusing the detector material itself. If all vertical strips or columns ofpixels are readout then it is straightforward to define multipleelectronic internal collimator configurations and observe the effects ofeach specific configuration on the reconstructed image.

Electronic internal collimator designs used in this invention are notlimited to combinations of detector elements such as vertical columns ofpixels. In one aspect, complex 2-D and 3-D electronic internalcollimators are used. It is straightforward to define complex 2-D and3-D electronic internal collimators by selectively ignoring individualdetector elements such as pixels to mimic conventional, mechanicalconverging, diverging, or parallel collimators as well as configurationsthat are impractical to implement with mechanical designs. The principleof creating an electronic internal collimator can be applied to bothface-on detectors and edge-on detectors.

Enhanced (SAR) Edge-on Imaging Probe Detector Geometries

In one aspect, the use of SAR edge-on semiconductor and scintillatordetectors in 2-D and 3-D imaging probes provides several benefits,including a reduction in the number of edge-on detector planes, thepotential for higher spatial resolution across the aperture, the abilityto correct for signal losses as a function of position, and an increasedactive detector volume. For example, with appropriate cooling a single1-D or 2-D SAR edge-on Ge detector plane that is approximately 20 mmthick can be used to provide a 2-D or 3-D imaging probe (including a3-D, Compton imaging probe) with a 20 mm×20 mm detector surface. Thesame imaging probe detector surface area can be provided by assemblingmultiple 1-D or 2-D SAR edge-on Ge detector planes with smaller apertureheights.

In one aspect, the use of detector planes with smaller aperture heightsexpands the list of viable candidate detector materials to includeSi(Li), CdZnTe, CdTe, HgI₂, etc. Improved SAR readout rates can beattained with 1-D edge-on semiconductor detectors when the monolithiccathode plane is divided into cathode readout strips that are parallelto the anode readout strips. An additional improvement in readout ratescan be attained (at the cost of increased complexity) by limitedsegmenting of the parallel cathode and anode strips in the manner shownin FIG 13 b. This modified, 2-D SAR edge-on detector is a limited, 3-DSAR edge-on detector. A further advantage to the limited segmentation ofanode and cathode strips is that the SAR capability can be used for onesegment level or both segment levels.

In one aspect, in a similar manner, a SAR edge-on scintillator rod orblock design is used to provide the same imaging probe detector surfacearea. SAR edge-on scintillator detectors can be implemented as limited,3-D SAR edge-on detectors in a straightforward manner. SAR edge-onsemiconductor and scintillator detectors can utilize a variablesemiconductor strip (or pixel) pitch or scintillator rod (or block)pitch, respectively. FIG 14 illustrates a perspective view of anenhanced (SAR), 3-D edge-on imaging probe detector comprised of a SARedge-on scintillator rod array 142 detector in which the first layer ofscintillator rods 128 can be a thin (a variable rod pitch along thevertical direction near the entrance surface) and of a material such asa plastic scintillator or low Z scintillator crystal in order to imagecharge particles or low energy gamma rays. The deeper layers ofscintillator rods are used to image high energy gamma rays. Data fromthe two photodetector arrays 100 is transmitted 103 to a computer forprocessing and display.

In one aspect, a number of scintillator rod implementations are used, aswell as two prominent scintillator block designs (3-D blocks and arraysof sheet blocks). Positive and negative factors to consider whenemploying block designs rather than rod designs include the lower costand increased active scintillator volume of blocks versus the increaseddead time and response uniformity problems near the periphery associatedwith scintillator blocks. Despite the increased costs associated with2-D scintillator sheet block arrays they may offer improved spatialresolution and readout rates compared to 3-D scintillator blocks asexplained in Nelson, U.S. Pat. Appl. No. 60/667,824. Multiple 3-D, SARedge-on scintillator blocks or sheet blocks (possibly using differentdimensions and/or different materials) can be stacked (layered). SARedge-on scintillator rod and block geometries can exploit a layereddesign that employs multiple scintillator materials. Furthermore,scintillator rod materials can be varied within a layer to optimize theresponse to a particular type of radiation or radiation energy. Forexample, the central region might detect photons or particles withspecific properties while the outer region would be used to detectdifferent particles or particle energies. There is no limitation withrespect to incorporating both SAR edge-on scintillator rod and blockdetector designs or SAR edge-on semiconductor and scintillator detectordesigns in an imaging probe.

Mixed Edge-on Imaging Probe Detector Geometries

In one aspect, the invention provides a mixed edge-on imaging probedetector comprised of a single layer, SAR scintillator rod array. FIG 15illustrates a perspective view of an exemplary mixed edge-on imagingprobe detector comprising a single layer, SAR scintillator rod array 122(using plastic scintillator or low Z scintillator crystal rods 123 andtwo photodetector arrays 100) for imaging charge particles or low energygamma rays. This exemplary SAR detector is stacked on top of an array ofbasic, 1-D edge-on semiconductor detectors 101 (or scintillatordetectors). Specific arrangements include (for example) a 4-quadrantedge-on detector with an internal collimator 120 or a 2-D edge-ondetector in an edge-on imaging probe (see FIGS. 12 a, 1 b).

Hybrid Edge-on Imaging Probe Detector Geometries

In one aspect, the invention provides SAR edge-on detector geometries orbasic edge-on detector geometries that are combined with face-ondetector geometries to create a hybrid edge-on imaging probe detector.For example, a Compton edge-on imaging probe based on a hybrid SARedge-on imaging probe detector would use a face-on, planar 2-D Si or Gearray as the Compton scatterer followed by a SAR edge-on scintillator orsemiconductor detector. In a different application the face-on, planar2-D Si or Ge array might be used to detect particles such as electron orpositrons (or a low energy photon) while the basic or SAR edge-onscintillator detectors might be used to detect high energy photons orother particles (possible in coincidence).

FIG 16 illustrates a perspective view of an exemplary hybrid edge-onimaging probe detector comprised of a relatively thin, 2-D, face-on Siarray 152 detector for charge particle stacked on top of an array ofbasic, 1-D edge-on semiconductor detectors 101 (or scintillatordetectors) arranged as (for example) a 4-quadrant edge-on detector withan internal collimator 120 (collimator not shown) in an edge-on imagingprobe (see FIG 12 b). An alternative configuration replaces the4-quadrant edge-on detector with a 2-D edge-on detector array (see FIG12 a). A variant of this design uses a face-on detector comprised of aplastic scintillator or low Z phosphor material coupled to a thinnedphotodiode array.

The imaging properties of edge-on (and face-on) detectors can beimproved by determining their spatial- and energy-dependent response toincident radiation. The calibration techniques developed forconventional face-on imaging probes, gamma cameras, and PET cameras canbe used with the edge-on imaging probe detectors describe herein. SARedge-on detectors require additional calibration in order to determinethe signal strength versus photon interaction location within asemiconductor or scintillator detector element (see Nelson, U.S. Pat.Appl. No. 60/667,824). Examples of applicable face-on DOI calibrationtechniques can be found in, e.g., in Huber J., et al., IEEE Trans. Nucl.Sci. Vol. 45, No. 3, pp. 1268-1272, June 1998 and Vaquero J., et al.,IEEE Trans. Med. Imag. Vol. 17, No. 6, pp. 967-978, December 1998. Inaddition, tracking algorithm techniques developed for particle detectorsand medical imaging can be used to estimate the validity of detectedevents and reduce signal noise.

Radiation converters or absorber materials can be integrated into anedge-on imaging probe detector. For example, a thin layer of absorbermaterial with appropriate k-edge properties might be used to attenuatelow energy photon radiation that is transmitted or scattered by a thin,face-on 2-D Si detector or scintillator detector. In a similar manner anabsorber material can be used to attenuate scattered incident electronsor secondary particles. A converter material might be used to createsecondary particles for an incident neutron or high energy photon. Theuse of non-detector materials (attenuators, converters, polarizers,etc.) to enhance the properties of an imaging detector is described,e.g., in Nelson, U.S. Pat. Appl. No. 60/667,824.

Although the embodiments of the present invention have been described interms of its use for nuclear medicine imaging probes (primarily photonsand electrons or positrons), the present invention may also be used innuclear medicine gamma camera, PET camera, and Compton camera edge-ondetector modules as well as in any industrial and scientificapplication, military and hazardous radiation material detectionapplications such as mine detection (described, e.g., in Nelson, U.S.Pat. No. 6,216,540), accelerator monitoring, and reactor monitoring.Thus, variations of the edge-on probe design can be made suitable forimaging photon with energies above 511 keV, charged particles, andneutral particles such as neutrons. For example, a basic, enhanced,mixed, or hybrid 3-D edge-on detector configuration can be incorporatedinto a mine detection probe or a soil contamination probe.

Consider the exemplary enhanced, 3-D edge-on probe detector of FIG 14.As a mine detection probe penetrates the soil the enhanced, 3-D edge-onprobe detector 142 can take measurements of radiation 107 enteringthrough a window with a moveable radiation shield in the tip of theprobe (incident upon its front face) or a window with a moveableradiation shield at the side of the probe (incident upon its side face147). Rotation of the entire probe or the 3-D edge-on probe detector(with a continuous side window) permits a 360 degree field of view at agiven depth along the z-axis.

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While the invention is susceptible to various modifications andalternative forms, specific examples thereof have been shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the invention is not to be limited to theparticular forms or methods disclosed, but to the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the appended claims.

What is claimed is:
 1. A segmented, position-sensitive readoutphotodetector in which each segment has its own independent readout,providing signal location information for edge-on and face-onscintillator detector modules.
 2. The segmented, position-sensitivereadout photodetector in which each segment has its own independentreadout of claim 1 wherein the photodetector comprises one of: a striparray PSAPD detector, a sub-strip array PSAPD detector, a sub-area arrayPSAPD detector, a mixed PSAPD detector, a sub-strip SDD detector or acombination thereof.
 3. An apparatus for detecting radiation comprising:(i) a segmented, position-sensitive readout photodetector in which eachsegment has its own independent readout, for edge-on and face-onscintillator detector modules as set forth in claim 1; (ii) theapparatus of (i), wherein the radiation detected is x-ray, gamma ray,and/or particle radiation; (iii) the apparatus of (i), wherein theapparatus further comprises, is operably linked to, or is part of anedge-on sub-aperture resolution (SAR) scintillator rod detector, asingle photon emission computed tomography (SPECT) device, a positronemission tomography (PET) device, a Compton probe detector or a Comptongamma camera.